A, a

[ey]
|

noun, plural A's or As, a's or as.

the first letter of the English alphabet, a vowel.
any spoken sound represented by the letter A or a, as in bake, hat, father, or small.
something having the shape of an A.
a written or printed representation of the letter A or a.
a device, as a printer's type, for reproducing the letter A or a.

Idioms

    from A to Z, from beginning to end; thoroughly; completely: He knows the Bible from A to Z.
    not know from A to B, to know nothing; be ignorant.

a

Measurements.

are; ares.

a

Symbol, Logic.

a

1
[uh; when stressed ey]

indefinite article

not any particular or certain one of a class or group: a man; a chemical; a house.
a certain; a particular: one at a time; two of a kind; A Miss Johnson called.
another; one typically resembling: a Cicero in eloquence; a Jonah.
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).
indefinitely or nonspecifically (used with adjectives expressing number): a great many years; a few stars.
one (used before a noun expressing quantity): a yard of ribbon; a score of times.
any; a single: not a one.

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

each; every; per: ten cents a sheet; three times a day.

Origin of a

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

a

3
[uh]

preposition

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.

Origin of a

3
Middle English; unstressed preconsonantal variant of of1

a

4
[uh]

auxiliary verb Pronunciation Spelling.

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.
Compare of2.

Origin of a

4
Middle English; phonetic variant of have

a

5
[uh, a, ah]

pronoun British Dialect.

Origin of a

5
Middle English a, ha

A

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

A

Symbol.

the first in order or in a series.
(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.
(sometimes lowercase) (in some school systems) a symbol designating the first semester of a school year.
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.
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.
(sometimes lowercase) the medieval Roman numeral for 50 or 500.Compare Roman numerals.
Chemistry. (formerly) argon.
Chemistry, Physics. mass number.
Biochemistry.
  1. adenine.
  2. alanine.
British. a designation for a motion picture recommended as suitable for adults.Compare AA(def 5), U(def 6), X(def 9).
a proportional shoe width size, narrower than B and wider than AA.
a proportional brassiere cup size, smaller than B and larger than AA.
a quality rating for a corporate or municipal bond, lower than AA and higher than BBB.

Å

Symbol, Physics.

a'

or a

[ah, aw]

adjective

Scot. all: for a' that.

a-

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).

Origin of a-

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

a-

2

a reduced form of the Old English preposition of: akin; afresh; anew.

Origin of a-

2
Middle English; see a3

a-

3

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).

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

variant of ab- before p and v: aperient; avert.

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

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.

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

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

A-

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

a.

1

Origin of a.

1
< Latin annō, ablative of annus

a.

2

Origin of a.

2
From the Latin word ante

a.

3

acre; acres.
ampere; amperes.
are; ares.
Baseball. assist; assists.

A.

1

Origin of A.

1
< Latin annō, ablative of annus

A.

2

Origin of A.

2
From the Latin word ante

A.

3

-a

1

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

-a

2

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.

-a

3

an ending of personal names forming feminines from masculines: Georgia; Roberta.

Origin of -a

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

-a

4

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

Origin of -a

4
probably generalized from the -a of magnesia

alpha

[al-fuh]

noun

the first letter of the Greek alphabet (A, α).
the vowel sound represented by this letter.
the first; beginning.
(initial capital letter) Astronomy. used to designate the brightest star in a constellation.
Chemistry. one of two or more isomeric compounds.
the first in a series of related items: frequently used in chemistry and physics.
Chiefly British. a mark or grade corresponding to an A.Compare beta(def 8), gamma(def 9).

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.
alphabetical: Put the files in alpha order.
Chemistry. pertaining or linked to the carbon atom closest to a particular group in an organic molecule.

Origin of alpha

< Latin < Greek álpha < Semitic; cf. aleph

Bronzino

[brawn-dzee-naw]

noun

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.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019


British Dictionary definitions for a

a

A

noun plural a's, A's or As

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

determiner (indefinite article; used before an initial consonant)

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

verb

an informal or dialect word for have they'd a said if they'd known

preposition

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

symbol for

acceleration
are(s) (metric measure of land)
atto-

A

symbol for

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
a human blood type of the ABO group, containing the A antigen
(in Britain) a major arterial roadthe A3 runs from London to Portsmouth
(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
mass number
the number 10 in hexadecimal notation
cards ace
chem argon (now superseded by Ar)
ampere(s)
Also: at ampere-turn
absolute (temperature)
(in circuit diagrams) ammeter
area
(in combination) atomican A-bomb; an A-plant
chem affinity
biochem adenine
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

abbreviation for

Austria (international car registration)

Word Origin for A

from Latin a (ffirmo) I affirm

Å

symbol for

angstrom unit

a-

1

before a vowel an-

prefix

not; without; opposite toatonal; asocial

Word Origin for a-

from Greek a-, an- not, without

a-

2

prefix

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

A.

abbreviation for

acre(s) or acreage
America(n)
answer

alpha

noun

the first letter in the Greek alphabet (Α, α), a vowel transliterated as a
British the highest grade or mark, as in an examination
(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
(modifier) denoting the dominant person or animal in a groupthe alpha male

Word Origin for alpha

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

Bronzino

noun

Il, real name Agnolo di Cosimo . 1503–72, Florentine mannerist painter

a'

aa or aw

determiner

Scot variants of all

Alpha

noun

(foll by the genitive case of a specified constellation) usually the brightest star in a constellationAlpha Centauri
communications a code word for the letter a
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
Online Etymology Dictionary, © 2010 Douglas Harper

Medicine definitions for a

a

abbr.

area
asymmetrical
specific absorption coefficient
systemic arterial blood (used as a subscript)
total acidity

A

abbr.

absorbance
alveolar gas (used as a subscript)
adenine
AMP (in polynucleotides)
ampere
angstrom
area

alpha

[ălfə]

n.

The first letter of the Greek alphabet.
The first one in a series; the beginning.
The first position from a designated carbon atom in an organic molecule at which an atom or radical group may be substituted.

adj.

Characterizing the atom or radical group that is closest to the functional group of atoms in an organic molecule.
Relating to one of two or more closely related substances, as in stereoisomers.
Relating to or characterizing a polypeptide chain that is one of five types of heavy chains present in immunoglobins.

a-

pref.

Without; not:acellular.

Å

abbr.

angstrom

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

Science definitions for a

A

Abbreviation of adenine, ampere, angstrom, area

Å

Abbreviation of angstrom

a-

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).
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.