[ uh, oh ]

  1. a shortened form of of, as in o'clock or will-o'-the-wisp.

  2. Chiefly Dialect. a shortened form of on.

Origin of o'

From Middle English; by shortening

Other definitions for O (2 of 15)


or o

[ oh ]

noun,plural O's or Os; o's or os or oes.
  1. the fifteenth letter of the English alphabet, a vowel.

  2. any spoken sound represented by the letter O or o, as in box, note, short, or love.

  1. something having the shape of an O.

  2. a written or printed representation of the letter O or o.

  3. a device, as a printer's type, for reproducing the letter O or o.

Other definitions for O (3 of 15)

[ oh ]

  1. (used before a name in direct address, especially in solemn or poetic language, to lend earnestness to an appeal): Hear, O Israel!

  2. (used as an expression of surprise, pain, annoyance, longing, gladness, etc.)

noun,plural O's.
  1. the exclamation “O.”

Origin of O

First recorded in 1125–75; Middle English, from Old French, from Latin ō

Words that may be confused with O

Other definitions for O (4 of 15)


  1. Grammar. object (def. 7).

  2. Old.

Other definitions for O (5 of 15)


  1. the fifteenth in order or in a series.

  2. the Arabic cipher; zero.

  1. (sometimes lowercase) the medieval Roman numeral for 11.: Compare Roman numerals.

  2. Physiology. a major blood group, usually enabling a person whose blood is of this type to donate blood to persons of group O, A, B, or AB and to receive blood from persons of group O.: Compare ABO system.

  3. Chemistry. oxygen.

Other definitions for O' (6 of 15)


  1. a prefix meaning “descendant,” in Irish family names: O'Brien; O'Connor.

Origin of O'

Representing Irish ó descendant, Old Irish au

Other definitions for o- (7 of 15)


  1. an abridgment of ortho-.

Other definitions for o- (8 of 15)


  1. variant of ob- before m:omission.

Other definitions for o- (9 of 15)


  1. variant of oo-: oidium.

Other definitions for -o- (10 of 15)


  1. the typical ending of the first element of compounds of Greek origin (as -i- is, in compounds of Latin origin), used regularly in forming new compounds with elements of Greek origin and often used in English as a connective irrespective of etymology: Franco-Italian; geography; seriocomic; speedometer.

Origin of -o-

Middle English (<Old French ) <Latin <Greek

Other definitions for -o (11 of 15)


  1. a suffix occurring as the final element in informal shortenings of nouns (ammo; combo; condo; limo; promo); -o also forms nouns, usually derogatory, for persons or things exemplifying or associated with that specified by the base noun or adjective (cheapo; pinko; sicko; weirdo; wino).

  2. a suffix occurring in colloquial noun or adjective derivatives, usually grammatically isolated, as in address: cheerio; kiddo; neato; righto.

Origin of -o

Perhaps originally the interjection O, appended to words as in def. 2; as a derivational suffix reinforced by clipped forms of words with -o- as a linking element (e.g., photo, stereo), by Rom nouns ending in o, and by personal nouns such as bimbo and bozo, of obscure origin

Other definitions for o. (12 of 15)


  1. pint.

Origin of o.

From the Latin word octārius

Other definitions for o. (13 of 15)


  1. octavo.

  2. off.

  1. old.

  2. only.

  3. order.

  4. Baseball. out; outs.

Other definitions for O. (14 of 15)


  1. (in prescriptions) a pint.

Origin of O.

From the Latin word octārius

Other definitions for O. (15 of 15)


  1. Ocean.

  2. octavo.

  1. October.

  2. Ohio.

  3. Old.

  4. Ontario.

  5. Oregon.

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2024

How to use o' in a sentence

British Dictionary definitions for o (1 of 8)



/ (əʊ) /

nounplural o's, O's or Os
  1. the 15th letter and fourth vowel of the modern English alphabet

  2. any of several speech sounds represented by this letter, in English as in code, pot, cow, move, or form

  1. another name for nought

British Dictionary definitions for o' (2 of 8)


/ (ə) /

  1. informal, or archaic shortened form of of a cup o' tea

British Dictionary definitions for O (3 of 8)


symbol for
  1. chem oxygen

  2. a human blood type of the ABO group: See universal donor

  1. logic a particular negative categorial proposition, such as some men are not married: often symbolized as SoP: Compare A, E, I 2

abbreviation for
  1. Australian slang offence

Origin of O

(for sense 3) from Latin (neg) o I deny

British Dictionary definitions for O (4 of 8)


/ (əʊ) /

  1. a variant spelling of oh

  2. an exclamation introducing an invocation, entreaty, wish, etc: O God!; O for the wings of a dove!

British Dictionary definitions for O'- (5 of 8)


  1. (in surnames of Irish Gaelic origin) descendant of: O'Corrigan

Origin of O'-

from Irish Gaelic ó, ua descendant

British Dictionary definitions for o- (6 of 8)


  1. short for ortho- (def. 4)

British Dictionary definitions for -o- (7 of 8)


connective vowel
  1. used to connect elements in a compound word: chromosome; filmography Compare -i-

Origin of -o-

from Greek, stem vowel of many nouns and adjectives in combination

British Dictionary definitions for -o (8 of 8)


  1. forming informal and slang variants and abbreviations, esp of nouns: wino; lie doggo; Jacko

Origin of -o

probably special use of oh

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

Scientific definitions for O


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