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definitions
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A, a

[ey]
noun, plural A's or As, a's or as.
  1. the first letter of the English alphabet, a vowel.
  2. any spoken sound represented by the letter A or a, as in bake, hat, father, or small.
  3. something having the shape of an A.
  4. a written or printed representation of the letter A or a.
  5. a device, as a printer's type, for reproducing the letter A or a.
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Idioms
  1. from A to Z, from beginning to end; thoroughly; completely: He knows the Bible from A to Z.
  2. not know from A to B, to know nothing; be ignorant.
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a

Measurements.
  1. are; ares.
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a

Symbol, Logic.
  1. universal affirmative.
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a

1
[uh; when stressed ey]
indefinite article
  1. not any particular or certain one of a class or group: a man; a chemical; a house.
  2. a certain; a particular: one at a time; two of a kind; A Miss Johnson called.
  3. another; one typically resembling: a Cicero in eloquence; a Jonah.
  4. one (used before plural nouns that are preceded by a quantifier singular in form): a hundred men (compare hundreds of men); a dozen times (compare dozens of times).
  5. indefinitely or nonspecifically (used with adjectives expressing number): a great many years; a few stars.
  6. one (used before a noun expressing quantity): a yard of ribbon; a score of times.
  7. any; a single: not a one.
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Origin of a

1
Middle English; orig. preconsonantal phonetic variant of an1

Usage note

In both spoken and written English the choice of a1 or an1 is determined by the initial sound of the word that follows. Before a consonant sound, a is used; before a vowel sound, an : a book, a rose; an apple, an opera. Problems arise occasionally when the following word begins with a vowel letter but actually starts with a consonant sound, or vice versa. Some words beginning with the vowel letter u and all words beginning with the vowel letters eu are pronounced with a beginning consonant sound, as if the first letter were y : a union; a European. Some other spellings that begin with a vowel letter may also stand for an initial consonant sound: a ewe; a ewer. The words one and once and all compounds of which they are the first element begin with a w sound: a one-room apartment; a once-famous actor.
The names of the consonant letters f, h, l, m, n, r, s, and x are pronounced with a beginning vowel sound. When these letters are used as words or to form words, they are preceded by an : to rent an L-shaped studio; to fly an SST. The names of the vowel letter u and the semivowel letters w and y are pronounced with a beginning consonant sound. When used as words, they are preceded by a : a U-turn; The plumber installed a Y in the line.
In some words beginning with the letter h, the h is not pronounced; the words actually begin with a vowel sound: an hour; an honor. When the h is strongly pronounced, as in a stressed syllable at the beginning of a word, it is preceded by a : a history of the Sioux; a hero sandwich. (In former times an was used before strongly pronounced h in a stressed first syllable: an hundred. ) Such adjectives as historic, historical, heroic, and habitual, which begin with an unstressed syllable and often with a silent or weakly pronounced h, are commonly preceded by an, especially in British English. But the use of a rather than an is widespread in both speech and writing: a historical novel; a habitual criminal. Hotel and unique are occasionally preceded by an, but this use is increasingly old-fashioned. Although in some dialects an has yielded to a in all cases, edited writing reflects usage as described above.

a

2
[uh; when stressed ey]
preposition
  1. each; every; per: ten cents a sheet; three times a day.
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Origin of a

2
orig. Middle English a, preconsonantal variant of on (see a-1); confused with a1

a

3
[uh]
preposition
  1. Pronunciation Spelling. a reduced, unstressed form of of (often written as part of a single, unhyphenated word): cloth a gold; time a day; kinda; sorta.
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Origin of a

3
Middle English; unstressed preconsonantal variant of of1

a

4
[uh]
auxiliary verb Pronunciation Spelling.
  1. a reduced, unstressed form of auxiliary have following some modals, as might, should, could, would, and must (usually written as part of a single, unhyphenated word): We shoulda gone.
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Compare of2.

Origin of a

4
Middle English; phonetic variant of have

a

5
[uh, a, ah]
pronoun British Dialect.
  1. he.
  2. she.
  3. it.
  4. they.
  5. I.
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Origin of a

5
Middle English a, ha

A

  1. Electricity. ampere; amperes.
  2. Physics. angstrom.
  3. answer.
  4. British. arterial (used with a road number to designate a major highway): Take the A525 to Ruthin.
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A

Symbol.
  1. the first in order or in a series.
  2. (sometimes lowercase) (in some grading systems) a grade or mark, as in school or college, indicating the quality of a student's work as excellent or superior.
  3. (sometimes lowercase) (in some school systems) a symbol designating the first semester of a school year.
  4. Music.
    1. the sixth tone in the scale of C major or the first tone in the relative minor scale, A minor.
    2. a string, key, or pipe tuned to this tone.
    3. a written or printed note representing this tone.
    4. (in the fixed system of solmization) the sixth tone of the scale of C major, called la.
    5. the tonality having A as the tonic note.
  5. Physiology. a major blood group, usually enabling a person whose blood is of this type to donate blood to persons of group A or AB and to receive blood from persons of O or A.Compare ABO system.
  6. (sometimes lowercase) the medieval Roman numeral for 50 or 500.Compare Roman numerals.
  7. Chemistry. (formerly) argon.
  8. Chemistry, Physics. mass number.
  9. Biochemistry.
    1. adenine.
    2. alanine.
  10. Logic. universal affirmative.
  11. British. a designation for a motion picture recommended as suitable for adults.Compare AA(def 5), U(def 6), X(def 9).
  12. a proportional shoe width size, narrower than B and wider than AA.
  13. a proportional brassiere cup size, smaller than B and larger than AA.
  14. a quality rating for a corporate or municipal bond, lower than AA and higher than BBB.
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Å

Symbol, Physics.
  1. angstrom.
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a'

or a

[ah, aw]
adjective
  1. Scot. all: for a' that.
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a-

1
  1. a reduced form of the Old English preposition on, meaning “on,” “in,” “into,” “to,” “toward,” preserved before a noun in a prepositional phrase, forming a predicate adjective or an adverbial element (afoot; abed; ashore; aside; away), or before an adjective (afar; aloud; alow), as a moribund prefix with a verb (acknowledge), and in archaic and dialectal use before a present participle in -ing (set the bells aringing); and added to a verb stem with the force of a present participle (ablaze; agape; aglow; astride; and originally, awry).
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Origin of a-

1
Middle English, late Old English; cf. a2, nowadays

a-

2
  1. a reduced form of the Old English preposition of: akin; afresh; anew.
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Origin of a-

2
Middle English; see a3

a-

3
  1. an old point-action prefix, not referring to an act as a whole, but only to the beginning or end: She arose (rose up). They abided by their beliefs (remained faithful to the end).
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Origin of a-

3
Middle English; Old English a- (unstressed), ǣ-, ā-, ō- (stressed; see abb, woof1, oakum), rarely or- (see ordeal) ≪ Germanic *uz- < unstressed Indo-European *uss- < *ud-s, akin to out; in some cases confused with a-4, as in abridge

a-

4
  1. variant of ab- before p and v: aperient; avert.
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Origin of a-

4
Middle English < Latin ā-, a- (variant of ab- ab-); in some words < French a- < Latin ab-, as in abridge

a-

5
  1. variant of ad-, used: (1) before sc, sp, st (ascend) and (2) in words of French derivation (often with the sense of increase, addition): amass.
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Origin of a-

5
Middle English, in some words < Middle French a- < Latin ad- prefix or ad preposition (see ad-), as in abut; in others < Latin a- (variant of ad- ad-), as in ascend

a-

6
  1. variant of an-1 before a consonant, meaning “not,” “without”: amoral; atonal; achromatic.
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A-

  1. atomic (used in combination): A-bomb; A-plant.
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a.

1
  1. year.
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Origin of a.

1
< Latin annō, ablative of annus

a.

2
  1. before.
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Origin of a.

2
From the Latin word ante

a.

3
  1. about.
  2. acre; acres.
  3. active.
  4. adjective.
  5. alto.
  6. ampere; amperes.
  7. anonymous.
  8. answer.
  9. are; ares.
  10. Baseball. assist; assists.
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A.

1
  1. year.
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Origin of A.

1
< Latin annō, ablative of annus

A.

2
  1. before.
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Origin of A.

2
From the Latin word ante

A.

3

-a

1
  1. a plural ending of nouns borrowed from Greek and Latin: phenomena; criteria; data; errata; genera.
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-a

2
  1. a feminine singular ending of nouns borrowed from Latin and Greek, also used in Neo-Latin coinages to Latinize bases of any origin, and as a Latin substitute for the feminine ending -ē of Greek words: anabaena; cinchona; pachysandra.
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-a

3
  1. an ending of personal names forming feminines from masculines: Georgia; Roberta.
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Origin of -a

3
< L feminine -a (see -a2), as Claudia, feminine of Claudius

-a

4
  1. a suffix designating the oxide of the chemical element denoted by the stem: alumina; ceria; thoria.
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Origin of -a

4
probably generalized from the -a of magnesia

alpha

[al-fuh]
noun
  1. the first letter of the Greek alphabet (A, α).
  2. the vowel sound represented by this letter.
  3. the first; beginning.
  4. (initial capital letter) Astronomy. used to designate the brightest star in a constellation.
  5. Chemistry. one of two or more isomeric compounds.
  6. the first in a series of related items: frequently used in chemistry and physics.
  7. Chiefly British. a mark or grade corresponding to an A.Compare beta(def 8), gamma(def 9).
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adjective
    1. (of an animal) having the highest rank in a dominance hierarchy: the alpha female of an elephant pack.
    2. being the most dominant, powerful, or assertive person in a particular group.
    See also alpha male.
  1. alphabetical: Put the files in alpha order.
  2. Chemistry. pertaining or linked to the carbon atom closest to a particular group in an organic molecule.
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Origin of alpha

< Latin < Greek álpha < Semitic; cf. aleph

Bronzino

[brawn-dzee-naw]
noun
  1. A·gno·lo (di Co·si·mo di Ma·ria·no) [ah-nyaw-law dee kaw-zee-maw dee mah-ryah-naw] /ˈɑ nyɔ lɔ di ˈkɔ zi mɔ di mɑˈryɑ nɔ/, 1502–72, Italian painter.
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Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for a

a

A

noun plural a's, A's or As
  1. the first letter and first vowel of the modern English alphabet
  2. any of several speech sounds represented by this letter, in English as in take, bag, calm, shortage, or cobra
  3. Also called: alpha the first in a series, esp the highest grade or mark, as in an examination
  4. from A to Z from start to finish, thoroughly and in detail
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a

1
determiner (indefinite article; used before an initial consonant)
  1. used preceding a singular countable noun, if the noun is not previously specified or knowna dog; a terrible disappointment
  2. used preceding a proper noun to indicate that a person or thing has some of the qualities of the one nameda Romeo; a Shylock
  3. used preceding a noun or determiner of quantitya cupful; a dozen eggs; a great many; to read a lot
  4. used preceding a noun indicating a concrete or abstract thing capable of being dividedhalf a loaf; a quarter of a minute
  5. (preceded by once, twice, several times, etc) each or every; peronce a day; fifty pence a pound
  6. a certain; oneto change policy at a stroke; a Mr Jones called
  7. (preceded by not) any at allnot a hope
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Compare an 1See the 1

a

2
verb
  1. an informal or dialect word for have they'd a said if they'd known
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a

3
preposition
  1. (usually linked to the preceding noun) an informal form of of sorta sad; a kinda waste
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a

4
symbol for
  1. acceleration
  2. are(s) (metric measure of land)
  3. atto-
  4. chess See algebraic notation
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A

symbol for
  1. music
    1. a note having a frequency of 440 hertz (A above middle C) or this value multiplied or divided by any power of 2; the sixth note of the scale of C major
    2. a key, string, or pipe producing this note
    3. the major or minor key having this note as its tonic
  2. a human blood type of the ABO group, containing the A antigen
  3. (in Britain) a major arterial roadthe A3 runs from London to Portsmouth
  4. (formerly, in Britain)
    1. a film certified for viewing by anyone, but which contains material that some parents may not wish their children to see
    2. (as modifier)an A film
  5. mass number
  6. the number 10 in hexadecimal notation
  7. cards ace
  8. chem argon (now superseded by Ar)
  9. ampere(s)
  10. Also: at ampere-turn
  11. absolute (temperature)
  12. (in circuit diagrams) ammeter
  13. area
  14. (in combination) atomican A-bomb; an A-plant
  15. chem affinity
  16. biochem adenine
  17. logic a universal affirmative categorical proposition, such as all men are mortal: often symbolized as SaPCompare E, I 2, O 1
    1. a person whose job is in top management, or who holds a senior administrative or professional position
    2. (as modifier)an A worker See also occupation groupings
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abbreviation for
  1. Austria (international car registration)
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Word Origin for A

from Latin a (ffirmo) I affirm

Å

symbol for
  1. angstrom unit
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a-

1

before a vowel an-

prefix
  1. not; without; opposite toatonal; asocial
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Word Origin for a-

from Greek a-, an- not, without

a-

2
prefix
  1. on; in; towardsafoot; abed; aground; aback
  2. literary, or archaic (used before a present participle) in the act or process ofcome a-running; go a-hunting
  3. in the condition or state ofafloat; alive; asleep
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A.

abbreviation for
  1. acre(s) or acreage
  2. America(n)
  3. answer
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alpha

noun
  1. the first letter in the Greek alphabet (Α, α), a vowel transliterated as a
  2. British the highest grade or mark, as in an examination
  3. (modifier)
    1. involving or relating to helium-4 nucleian alpha particle
    2. relating to one of two or more allotropes or crystal structures of a solidalpha iron
    3. relating to one of two or more isomeric forms of a chemical compound, esp one in which a group is attached to the carbon atom to which the principal group is attached
  4. (modifier) denoting the dominant person or animal in a groupthe alpha male
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Word Origin for alpha

via Latin from Greek, of Phoenician origin; related to Hebrew āleph, literally: ox

Bronzino

noun
  1. Il, real name Agnolo di Cosimo . 1503–72, Florentine mannerist painter
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a'

aa or aw

determiner
  1. Scot variants of all
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Alpha

noun
  1. (foll by the genitive case of a specified constellation) usually the brightest star in a constellationAlpha Centauri
  2. communications a code word for the letter a
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Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for a

1

indefinite article, mid-12c., a variation of Old English an (see an) in which the -n- began to disappear before consonants, a process mostly complete by mid-14c. The -n- also was retained before words beginning with a sounded -h- until c.1600; it still is retained by many writers before unaccented syllables in h- or (e)u-, but is now no longer normally spoken as such. The -n- also lingered (especially in southern England dialect) before -w- and -y- through 15c.

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2

as in twice a day, etc., from Old English an "on," in this case "on each." The sense was extended from time to measure, price, place, etc. The habit of tacking a onto a gerund (as in a-hunting we will go) died out 18c.

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a-

3

prefix meaning "not," from Greek a-, an- "not," from PIE root *ne "not" (see un-).

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alpha

n.

c.1300, from Latin alpha, from Greek alpha, from Hebrew or Phoenician aleph (see aleph). The Greeks added -a because Greek words cannot end in most consonants. Sense of "beginning of anything" is from late 14c., often paired with omega (last letter in the Greek alphabet) as "the end." Sense of "first in a sequence" is from 1620s. Alpha male was in use by c.1960 among scientists studying animals; applied to humans in society from c.1992.

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a-

1

in native (derived from Old English) words, it most commonly represents Old English an "on" (see a (2)), as in alive, asleep, abroad, afoot, etc., forming adjectives and adverbs from nouns; but it also can be Middle English of, as in anew, abreast (1590s); or a reduced form of Old English past participle prefix ge-, as in aware; or the Old English intensive a-, as in arise, awake, ashame, marking a verb as momentary, a single event. In words from Romanic languages, often it represents Latin ad- "to, at."

[I]t naturally happened that all these a- prefixes were at length confusedly lumped together in idea, and the resultant a- looked upon as vaguely intensive, rhetorical, euphonic, or even archaic, and wholly otiose. [OED]
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a-

2

prefix meaning "not," from Latin a-, short for ab "away from" (e.g. avert), or its cognate, Greek a-, short for apo "away from, from," both cognate with Sanskrit apa "away from," Gothic af, Old English of (see apo-).

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Online Etymology Dictionary, © 2010 Douglas Harper

a in Medicine

a

abbr.
  1. area
  2. asymmetrical
  3. specific absorption coefficient
  4. systemic arterial blood (used as a subscript)
  5. total acidity
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A

abbr.
  1. absorbance
  2. alveolar gas (used as a subscript)
  3. adenine
  4. AMP (in polynucleotides)
  5. ampere
  6. angstrom
  7. area
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alpha

(ălfə)
n.
  1. The first letter of the Greek alphabet.
  2. The first one in a series; the beginning.
  3. The first position from a designated carbon atom in an organic molecule at which an atom or radical group may be substituted.
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adj.
  1. Characterizing the atom or radical group that is closest to the functional group of atoms in an organic molecule.
  2. Relating to one of two or more closely related substances, as in stereoisomers.
  3. Relating to or characterizing a polypeptide chain that is one of five types of heavy chains present in immunoglobins.
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a-

pref.
  1. Without; not:acellular.
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Å

abbr.
  1. angstrom
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

a in Science

A

  1. Abbreviation of adenine, ampere, angstrom, area
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Å

  1. Abbreviation of angstrom
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a-

  1. A prefix meaning “without” or “not” when forming an adjective (such as amorphous, without form, or atypical, not typical), and “absence of” when forming a noun (such as arrhythmia, absence of rhythm). Before a vowel or h it becomes an- (as in anhydrous, anoxia).
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.