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  • O
    O
    noun
    the fifteenth letter of the English alphabet, a vowel.
  • o'
    o'
    preposition
    a shortened form of of, as in o'clock or will-o'-the-wisp.
  • O'
    O'
    a prefix meaning “descendant,” in Irish family names.
  • o-
    o-
    an abridgment of ortho-.
  • -o
    -o
    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 ).
  • o.
    o.
    abbreviation
    pint.
  • -o-
    -o-
    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.
  • O.
    O.
    abbreviation
    (in prescriptions) a pint.
  • o
    o
    noun
    the 15th letter and fourth vowel of the modern English alphabet
  • O'-
    O'-
    prefix
    (in surnames of Irish Gaelic origin) descendant of
Synonyms

O

1 American  
[oh] / oʊ /
Or o

noun

  • O's,
    plural
  • Os,
    plural
  • o's,
    plural
  • os,
    plural
  • oes
    plural
  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 .

  3. something having the shape of an O .

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

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


O 2 American  
[oh] / oʊ /

interjection

  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

  • O's
    plural
  1. the exclamation “O.”

O 3 American  

abbreviation

  1. Grammar. object.

  2. Old.


O 4 American  
Symbol.
  1. the fifteenth in order or in a series.

  2. the Arabic cipher; zero.

  3. (sometimes lowercase) the medieval Roman numeral for 11.

  4. 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.

  5. Chemistry. oxygen.

  6. Logic. particular negative.


o' 5 American  
[uh, oh] / ə, oʊ /

preposition

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

  2. Chiefly Dialect. a shortened form of on.


O' 6 American  
  1. a prefix meaning “descendant,” in Irish family names.

    O'Brien; O'Connor.


o- 7 American  
Chemistry.
  1. an abridgment of ortho-.


o- 8 American  
  1. variant of ob- before m:

    omission.


o- 9 American  
  1. variant of oo-.

    oidium.


-o 10 American  
  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.


o. 11 American  

abbreviation

  1. pint.


o. 12 American  

abbreviation

  1. octavo.

  2. off.

  3. old.

  4. only.

  5. order.

  6. Baseball. out; outs.


-o- 13 American  
  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.


O. 14 American  

abbreviation

  1. (in prescriptions) a pint.


O. 15 American  

abbreviation

  1. Ocean.

  2. octavo.

  3. October.

  4. Ohio.

  5. Old.

  6. Ontario.

  7. Oregon.


O 1 British  

symbol

  1. chem oxygen

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

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

"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

abbreviation

  1. slang offence

"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
o 2 British  
/ əʊ /

noun

  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

  3. another name for nought

"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

O 3 British  
/ əʊ /

interjection

  1. a variant spelling of oh

  2. an exclamation introducing an invocation, entreaty, wish, etc

    O God!

    O for the wings of a dove!

"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

O'- 4 British  

prefix

  1. (in surnames of Irish Gaelic origin) descendant of

    O'Corrigan

"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

-o 5 British  

suffix

  1. forming informal and slang variants and abbreviations, esp of nouns

    wino

    lie doggo

    Jacko

"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

-o- 6 British  
  1. used to connect elements in a compound word Compare -i-

    chromosome

    filmography

"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

o- 7 British  

prefix

  1. short for ortho-

"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

o' 8 British  
/ ə /

preposition

  1. informal shortened form of of

    a cup o' tea

"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

Other Word Forms

Noun Inflected Forms


Etymology

Origin of O2

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

Origin of o'5

From Middle English; by shortening

Origin of O'6

Representing Irish ó descendant, Old Irish au

Origin of -o10

Perhaps originally the interjection O, appended to words as in -o 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

Origin of o.11

From the Latin word octārius

Origin of -o-13

Middle English (< Old French ) < Latin < Greek

Origin of O.14

From the Latin word octārius


Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

See Examples For:

The MAL story also illustrates how much complexity is hidden behind the familiar letters A, B, AB and O.

From Science Daily ● Sep. 19, 2026

A delicious word salad: How many words can you create with the letters Y, B, O, F, U, and N?

From Slate ● Aug. 18, 2026

It also gives non-Asian chorus members a reason to be present at Butterfly’s wedding, though having a group of American ladies sing the invocation “O Kami! O Kami!” from song sheets seemed peculiar.

From The Wall Street Journal ● Aug. 17, 2026

Supplies of every blood type are currently needed, but especially O positive, which is considered a universal blood type and can be given to people in an emergency when theirs is unknown.

From BBC ● Jul. 29, 2026

“I am a suppliant at your knees, O Queen,” he said.

From "Mythology: Timeless Tales of Gods and Heroes" by Edith Hamilton

“But also look at a Prince album like Sign o’ the Times, which is a masterpiece, but some of Prince’s best ideas on that album are mistakes.”

From The Wall Street Journal ● Oct. 22, 2026

However, “in past El Niño events, we’ve seen similar-looking Portuguese man o’ war, a very rare visitor to our waters, washing up on our beaches.

From Los Angeles Times ● Jun. 15, 2026

“Coffee badging”—going to the office just long enough to show your face and grab a cup o’ joe—was a popular workaround.

From The Wall Street Journal ● Dec. 30, 2025

Amelie McCann said Julia Wandelt had told her she had memories of playing Ring a Ring o' Roses with her and feeding her brother Sean.

From BBC ● Oct. 9, 2025

“She’ll happen do better for him nor ony o’ t’ grand ladies.”

From "Jane Eyre" by Charlotte Brontë

Former basketball player Shaquille O’ Neal is also a high-profile investor.

From MarketWatch ● Nov. 19, 2025

But Heart O’ the Hills confirmed that its camp director, Jane Ragsdale, is one of the flood’s victims .

From Salon ● Jul. 7, 2025

Girls summer camp Heart O’ the Hills is just a mile north of Camp Mystic.

From Salon ● Jul. 7, 2025

Heart O' the Hills is another all-girls' camp that sits along the Guadalupe River, and it was right in the path of Friday's flood.

From BBC ● Jul. 5, 2025

After a single trip to the supermarket, the refrigerator and the cupboards fill with familiar labels: Skippy, Hood, Bumble Bee, Land O’ Lakes.

From "The Namesake" by Jhumpa Lahiri

At week's end a Russian delegation got the signatures of the leaders of Kazakhstan on a similar agreement-to-try-t o- agree.

From Time Magazine Archive

Phenol-2,4-disulphonic acid is prepared from o- or p-phenolsulphonic acid, whereas phenol-2,4,6-trisulphonic acid is prepared directly from phenol by heating with concentrated sulphuric acid in presence of phosphorus pentoxide.

From Synthetic Tannins by Georg Grasser

Quintilianus saieth, that Ethopœia is a imitacion of o- ther meane maners: whom the Grekes dooe calle, not onelie Ethopœia, but mimesis, & this is in the maners, and the fact.

From A booke called the Foundacion of Rhetorike because all other partes of Rhetorike are grounded thereupon, euery parte sette forthe in an Oracion vpon questions, verie profitable to bee knowen and redde by Richard Rainolde

And trewelie, if there be any // and in no o- good in them, it is either lerned, borowed, or // ther tong. stolne, from some one of those worthie wittes of Athens.

From The Schoolmaster by Roger Ascham

B-- -o-ey -o---- -o yo- -ro- old --ore le-- ---a-d --a- ---y --are -or -olle----- -or yo--o r--- --ll -all o- yo- ---r-day a- -o-r -e-.

From The Crevice by Will Grefé

I don't think the "-e" should eliminate the existing "-o" and the "-a."

From Salon ● Sep. 26, 2022

Usually words ending in "-o" are masculine and those ending in "-a" are feminine, but there are many common words that break those gender rules, like "la mano," the word for "hand."

From Salon ● Sep. 26, 2022

The -o suffix traces back to old comic strip characters with names like Knocko and Groucho.

From Slate ● Mar. 31, 2020

Knocko, Peddlo, Henpecko, and the rest became so popular that the -o suffix soon spread to words up and down the English language.

From Slate ● Mar. 31, 2020

I knew perfectly well why, but I didn’t know how -o put it.

From "Boy: Tales of a Childhood" by Roald Dahl

The Illumina-based genome assemblies for P. o. curtisi, P. o. wallikeri, and P. malariae-like were performed using MaSURCA30 for samples PocGH01, PowCR01, and PmlGA01 respectively.

From Nature ● Jan. 24, 2017

This gene family was recently named KELT7, and we confirm the 8 copies present in P. o. wallikeri, but show that P. o. curtisi has 9 copies, two of which are pseudogenes.

From Nature ● Jan. 24, 2017

Reality is that you are giving up your family time by doing the o. t. when they need you at work. 

From Time ● May 3, 2013

“If you dey come give am ticket to leave this here country, I will disappear o. I will not even stop home for pick my bag.”

From Washington Post

“Haba! I don’t text and drive o. I text when I’m not driving,” she said.

From "Americanah" by Chimamanda Ngozi Adichie

Thus masc. -o- stems show palatal modification, e.g. corn, “horn,” plur. cyrn < *kornī; the plural ending of -u- stems, O. Gaulish -oves, gives O.W. -ou, Mid.

From Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 5 "Cat" to "Celt" by Various

District Court Judge David O. Carter ordered the VA to build about 2,500 units of temporary and permanent housing in addition to the 1,200 required in the earlier lawsuit.

From Los Angeles Times ● Sep. 11, 2026

Thankfully, Curry did not allow any eerie rumors to deter him from securing the home, which was originally built in 1922, having been designed by acclaimed architect Stiles O. Clements.

From MarketWatch ● Aug. 31, 2026

The Senate opened debate this week on the late South Carolina senator’s legacy legislation—the Lindsey O. Graham Sanctioning Russia and Iran Act—by an overwhelming 86–12 vote.

From Slate ● Aug. 1, 2026

And if he’s going to be a senator, he says, he needs to lock down a Jackie O. – not a Marilyn.

From Salon ● Jul. 6, 2026

There was nobody to do it except Uncle O. V., and he was the bereaved too.

From "The Bluest Eye" by Toni Morrison

Shane Graham, chief executive of Te Rūnanga o Ngāti Rārua, a Māori authority, said the return was a momentous occasion.

From BBC ● Oct. 10, 2026

“LAHD is very excited about the opportunities ...t o produce more affordable housing and stabilize the city’s housing stock,” said Tiena Johnson Hall, the housing department’s general manager.

From Los Angeles Times ● Sep. 23, 2026

Allow me to sing, o Muse, of a recent dinner conversation about “The Odyssey.”

From Salon ● Aug. 2, 2026

Mr. Brownlee’s tenor proved rock-solid in Arturo’s demanding music, from his exquisitely relaxed, almost languid opening aria, “A te, o cara,” to some punishing high Fs.

From The Wall Street Journal ● Jan. 2, 2026

“Shush, shush, o zugo,” she said, feeling a little theatrical.

From "Half of a Yellow Sun" by Chimamanda Ngozi Adichie

“He doesn’t have a body that you would be like, ‘Wow, this guy’s a specimen,’” said Johnny Olson, the owner of Johnny O’s.

From The Wall Street Journal ● Sep. 30, 2026

Barely a week after tying the knot with Taylor Swift in July, Kansas City Chiefs tight end Travis Kelce was back at work inside Johnny O’s Gymnasium in Florida.

From The Wall Street Journal ● Sep. 30, 2026

Both senior managers were subsequently disciplined by Google for witnessing Mr O's conduct and failing to intervene, before later being made redundant.

From BBC ● Mar. 10, 2026

Carson Palmer’s coaching staff, filled with former NFL players like himself, have shown they can teach, lead and handle X’s and O’s.

From Los Angeles Times ● Nov. 23, 2025

“I knows what them is,” he said, putting his finger on the X’s and O’s.

From "Code Talker: A Novel About the Navajo Marines of World War Two" by Joseph Bruchac

In 1988, he founded Luaka Bop, a record label whose influential compilations have introduced American audiences to lesser-known classics of world pop and psychedelia, such as Brazil’s Os Mutantes.

From The Wall Street Journal ● Oct. 9, 2026

"The Dutch experience in my opinion offers a warning for Canada," Os cautioned.

From BBC ● May 15, 2026

Another hurdle that Os had to overcome in her career is an ongoing stigma placed on influencers-turned-pop stars.

From Los Angeles Times ● Mar. 20, 2026

On the personal side, Os is also relishing her relationship with Peso Pluma.

From Los Angeles Times ● Mar. 20, 2026

She’d been fourteen, and her family had been summering on the coast of West Ravka, enjoying the seaside and performing in a carnival on the outskirts of Os Kervo.

From "Six of Crows" by Leigh Bardugo

Like other Romance languages, Spanish divides most endings of nouns into masculine o’s or feminine a’s.

From Washington Times ● Dec. 12, 2021

Plosives, or stops, convey “slower” and “bigger” — as do vowels that are voiced at the back of the throat, like the o in “token” or the double o’s in “food.”

From New York Times ● Jan. 15, 2015

Texting and Millennials The phone holds a million x’s and o’s.

From Forbes ● Jun. 5, 2013

A young executive named Mark Shapiro, now gone, pushed it as a way to broaden the network's appeal beyond "the hard x's and o's crowd."

From Slate ● Jun. 1, 2011

The Cranes Conquer America was written at the top in Emily’s eight-year-old scrawl, back when she was into putting smiley faces inside her e’s, o’s, and o’s.

From "Book Scavenger" by Jennifer Chambliss Bertman

Dreyfus pleased his friends no better than his :oes: he irked them by not becoming a "Dreyfusard."

From Time Magazine Archive

Nad oes wedd na moes, masw ynyd yw’n gwlad, Nad oes mad eithr gwad a gwyd.

From Some Specimens of the Poetry of the Ancient Welsh Bards by Evan Evans

Ir wyfi yn meddwl nad oes neb a ryfygei gymmeryd y fath orchest arno. 

From Some Specimens of the Poetry of the Ancient Welsh Bards by Evan Evans

I was taking a lesson in Welsh pronunciation some time ago, and uttered the phrase "yn oes oesodd"—from ages to ages.

From Far Off Things by Arthur Machen

Cymmrodedd fy llyw lluoedd beri, Nid oes rwyf eirioes, aer dyfysgu, Cymro yw haelryw o hil Beli hir,    Yn herwydd i brofi.

From Some Specimens of the Poetry of the Ancient Welsh Bards by Evan Evans

A new Longevity Preparedness Index from John Hancock and MIT AgeLab os based on a survey of over 1,300 adults and focused on eight areas such as finance, home, health and community.

From MarketWatch ● Dec. 12, 2025

She first broke through with 2016’s “Remonta,” an album she recorded with her former band Liniker e os Caramelows.

From Los Angeles Times ● Oct. 8, 2025

Ambos os programas são “fundamentais para entender a expansão agrícola no Brasil e as emissões de carbono do desmatamento na Amazônia,” diz Douglas Morton, especialista em sensoriamento remoto do Goddard Space Flight Center da NASA.

From Science Magazine ● May 26, 2022

Hours later, Kelly posts bail and os released from jail in Chicago.

From Seattle Times ● Aug. 18, 2021

Newton disliked infinitesimals, the little os in his fluxion equations that sometimes acted like zeros and sometimes like nonzero numbers.

From "Zero: The Biography of a Dangerous Idea" by Charles Seife

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