from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun The 15th letter of the modern English alphabet.
  • noun Any of the speech sounds represented by the letter o.
  • noun The 15th in a series.
  • noun Something shaped like the letter O.
  • noun One of the four major blood groups in the ABO system. Individuals with this blood group have neither A nor B antigens on the surface of their red blood cells, and have both anti-A and anti-B antibodies in their blood serum.
  • noun A zero.

from The Century Dictionary.

  • The usual “connecting vowel,” properly the stem-vowel of the first element, of compound words taken or formed from the Greek, as in acr-o-lith, chrys-o-prase, mon-o-tone, prot-o-martyr, etc.
  • Same as one.
  • Same as a, the indefinite article.
  • A prefix common in Irish surnames, equivalent to Mac-in Gaelic and Irish surnames (see Mac), meaning ‘son,’ as in O'Brien, O'Connor, O'Donnell, O'Sullivan, son of Brien, Connor, Donnell, etc.
  • noun An exclamation or lamentation.
  • noun Same as ho.
  • An abbreviated form of of, now commonly written o'.
  • An abbreviation
  • in electricity, of ohm;
  • of Ohio;
  • of only;
  • of opening of the circuit;
  • in psychology, of observer.
  • The fifteenth letter and fourth vowel in our alphabet.
  • It thus appears that the belief, not uncommonly held, that O represents, and is imitated from, the rounded position of the lips in its utterance, is a delusion. The historical value of the letter (as already noticed) is that of our o, in note, etc., whether of both long and short quantities, as in Latin and the earliest Greek, or of short only, as in Greek after the addition to that alphabet of a special sign for long o (namely omega, Ω, ω). This vowel-sound, the name-sound of o, is found in English usage only with long quantity in accented syllables. There is no closely corresponding short vowel in standard English, but only in dialectal pronunciation, as in the New England utterance of certain words (much varying in number in different individuals): for example, home, whole, none. What we call “short o” (in not, on, etc.) is a sound of altogether different quality, very near to a true short ä (that is, a short utterance corresponding to the a of arm, father), but verging slightly toward the “broad” a (â) or o (ô) of laud, lord. “Short o” has a marked tendency to take on a “broader” sound, especially before r, and especially in America: hence the use, in the respellings of this work, of ô, which varies in different mouths from the full sound of â to that of ŏ. After these three values of the character, the next most common one is that of the oo-sonnd, the original and proper sound of u (represented in this work by ö), as in move, with the nearly corresponding short sound (marked u) in a few words, as wolf, woman. All these vowel-sounds partake of what is usually called a “labial” or a “rounded” character: that is to say, there is involved in their utterance a rounding and closing movement of the lips (and, it is held, of the whole mouth-cavity), in different degrees — least of all in ŏ, more and more in â, ō, u, ö; in the last, carried to its extreme, no closer rounding and approximation being possible. The labial action helps to give the vowel-sounds in question their fully distinctive character; but it can be more or less slighted without leaving them unrecognizable, and, in the generally indifferent habit of English pronunciation, is in a degree neglected, even in accented syllables, and yet more in unaccented. Our “long ō,” it should be added, regularly ends with a vanishing sound of oo (ö), as our ā with one of ē. O also has in many words the value of the “neutral” vowels of hut, hurt: for example, in son, come, love, work. O is further a member of several very common and important digraphs: thus, oo, the most marked representative of the ö-sound (in moon, rood, etc.), but also pronounced as u (book, look, etc.) and ŭ (blood, etc.); ou (in certain situations ow), oftenest representing a real diphthong (in out, sound, now, etc.), but also a variety of other sounds (as in through, could, ought, rough); oi (in certain situations oy), standing for a real diphthongal sound of which the first element is the “broad” o- or a-sound (for example, point, boy); oa (load, etc.), having the “long” o-sound; others, as eo (variously pronounced, as in people, yeoman, jeopard), oe (in foe, does, etc.), are comparatively rare.
  • As a medieval Roman numeral, 11.
  • As a symbol: In medieval musical notation, the sign of the tempus perfectum — that is, of triple rhythm. See mensurable music, under mensurable.
  • In modern musical notation, a null (which see)
  • In chem., the symbol of oxygen.
  • In logic, the symbol of the particular negative proposition. See A, 2 .
  • An abbreviation: Of old: as, in O. H. G., Old High German; O. T., Old Testament.
  • Of the Middle Latin octavius, a pint.
  • [lowercase] In a ship's log-book, of overcast.
  • Pl. o's, oes (ōz). Anything circular or approximately so, as resembling the shape of the letter o, as a spangle, the circle of a theater, the earth, etc.
  • An arithmetical cipher; zero: so called from its form.
  • An abbreviated form of on. Commonly written o'.
  • A common interjection expressing surprise, pain, gladness, appeal, entreaty, invocation, lament, etc., according to the manner of utterance and the circumstances of the case.

from the GNU version of the Collaborative International Dictionary of English.

  • noun The letter O, or its sound.
  • noun Something shaped like the letter O; a circle or oval.
  • noun rare A cipher; zero.
  • adjective obsolete One.
  • interjection An exclamation used in calling or directly addressing a person or personified object; also, as an emotional or impassioned exclamation expressing pain, grief, surprise, desire, fear, etc.
  • interjection exclamations expressive of various emotions, but usually promoted by surprise, consternation, grief, pain, etc.
  • O, the fifteenth letter of the English alphabet, derives its form, value, and name from the Greek O, through the Latin. The letter came into the Greek from the Phœnician, which possibly derived it ultimately from the Egyptian. Etymologically, the letter o is most closely related to a, e, and u; as in E. bone, AS. bān; E. stone, AS. stān; E. broke, AS. brecan to break; E. bore, AS. beran to bear; E. dove, AS. dūfe; E. toft, tuft; tone, tune; number, F. nombre.
  • Among the ancients, O was a mark of triple time, from the notion that the ternary, or number 3, is the most perfect of numbers, and properly expressed by a circle, the most perfect figure.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun The fifteenth letter of the English alphabet, called o and written in the Latin script.
  • noun The ordinal number fifteenth, derived from this letter of the English alphabet, called o and written in the Latin script.
  • noun The name of the Latin script letter O/o.
  • noun A zero (used in reading out numbers).
  • noun The fifteenth letter of the basic modern Latin alphabet.
  • noun close-mid back rounded vowel
  • interjection archaic The English vocative particle, used before a pronoun or the name of a person or persons to mark direct address.
  • interjection Alternative form of oh.


Sorry, no etymologies found.


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  • Without referring to geometry we can see at a glance by Fig. 172, where we have simply turned the square _o o o o_ on its centre so that its angles touch the sides of the outer square, that it is exactly half of square _ABEF_, since each quarter of it, such as

    The Theory and Practice of Perspective 1876

  • By drawing _ff_, _f·f_ passing through the diagonals we get the four points _o o o o_ through which to draw the smaller square.

    The Theory and Practice of Perspective 1876

  • $$@@$@$$@ $$@ $@$ $@$@$o$$@$$ $@$$o o$$@$ % @$@ $$@$ $ $$$ @

    The Mortal Kombat III FAQ Version 1.1 by John Coleman 1994

  • I'm just a lump o 'love yahooBuzzArticleHeadline =' I\'m just a lump o\ 'love'; yahooBuzzArticleSummary = 'Article: Valentine\'s humor.'

    I'm just a lump o' love 2009

  • April 26, 2008 at 2:17 pm o noes…i iz so lat, n ders brains n thots rollin all ober de flor…..o teh hoomanitees….u ned mor dan CCC, u ned cwoot reshushitaton teknishuns n resku goggies n … n… quik, call Cadboorees, ders a wurldwide dysasterz!

    Rwar? - Lolcats 'n' Funny Pictures of Cats - I Can Has Cheezburger? 2008

  • February 9, 2008 at 5:51 am o/…Aaaaaaah-vay Mareeeeeeeeeaaaaaaah….o/

    OMG - Lolcats 'n' Funny Pictures of Cats - I Can Has Cheezburger? 2008

  • It was strange to hear the pipes of the Highlanders skirl shrilly through old Boulogne, and to catch the sound of English voices in the clarion notes of the "Marseillaise," but, strangest of all to French ears, to listen to that new battle-cry, "Are we down-hearted?" followed by the unanswerable "No -- o-- o!" of every regiment.

    Tommy Atkins at War As Told in His Own Letters James Alexander Kilpatrick

  • "So -- o-- o are we," gasped Grace, staggering to her feet, and almost instantly landing on her back on the ground where the wind had hurled her.

    Grace Harlowe's Overland Riders on the Great American Desert Jessie Graham [pseud.] Flower

  • I’m thinking, for the laird’s servant—that’s no to say his body-servant, but the helper like—rade express by this e’en to fetch the houdie, and he just stayed the drinking o’ twa pints o’ tippeny, & tcedil; o tell us how my leddy was ta’en wi’ her pains.

    Chapter I 1917

  • "Whoop! whoo -- o-- o!" they screeched, yelling like Indians; and their leader, who was uglier looking than any of his followers, cried out:

    John Dough And The Cherub Baum, L. Frank 1906


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  • I've read - somewhere - that this word has been used (once, in the past tense) as a verb meaning 'to decorate with small circles'.

    October 22, 2007

  • Kind of like Xing, or however you spell that? Like when you X something out?

    October 22, 2007

  • suggests 'x-ing' or 'x'ing', so maybe the forms of 'to O' would be better as O-es, O-ing, O-ed.

    October 23, 2007

  • Agreed, they should be consistent, I would think. But I don't really like the two forms you cited, personally, because x-ing is what you see on railroad crossing signs, and so I just head-pronounce it crossing. And x ing is totally weird: where else do you find a space between a verb and its -ing suffix? That can't be right!

    October 23, 2007

  • I head-pronounced 'Xing' as 'crossing' once I grasped the sense you intended; it also seems to be the name of a company, among other things...

    October 23, 2007

  • That's true, Xing is also a common Chinese name, and it's pronounced "zing." So, I guess we can't win either way. ;-)

    October 23, 2007

  • O. Chemical element symbol for Oxygen.

    December 16, 2007

  • For some reason, some of the examples are for Latino (interpreted as Latin o?).

    November 18, 2009

  • C'mon, buy d' O Ernie

    November 8, 2010