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.

Chemistry. oxygen.

EXPAND

Logic. particular negative.

COLLAPSE

preposition

an abbreviated form of of, as in o'clock or will-o'-the-wisp.

an abbreviated form of on.

Origin:
Middle English; by shortening.

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

Origin:
representing Irish ó descendant, Old Irish au

Chemistry.

an abridgment of ortho-.

variant of ob- before m: omission.

variant of oo-: oidium.

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.

Compare -i-.

Origin:
Middle English (< Old French ) < Latin < Greek

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).

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

Origin:
perhaps orig. 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

Ocean.

(in prescriptions) a pint. Origin:
< Latin octārius

pint. Origin:
< Latin octārius

Baseball. out; outs.

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Link To O

Collins

World English Dictionary

o or O (əʊ)

—n , pl o's, O's, 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
3.	another name for nought

O or O

—n

o or O (əʊ)

—n , pl o's, O's, 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
3.	another name for nought

O or O

—n

O¹

—*symbol for*
1.	chem oxygen
2.	See universal donor a human blood type of the ABO group
3.	logic A E Compare I a particular negative categorial proposition, such as some men are not married: often symbolized as SoP

—*abbreviation for*
4.	slang (Austral) offence

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

O² (əʊ)

—*interj*
1.	a variant spelling of oh
2.	an exclamation introducing an invocation, entreaty, wish, etc: O God!; O for the wings of a dove!

o' (ə)

—*prep*
	informal, archaic or shortened form of of : a cup o' tea

Collins English Dictionary - Complete & Unabridged 10th Edition
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Etymonline

Word Origin & History

interj. of fear, surprise, admiration, etc., see oh.

EXPAND

blood type, 1926, originally "zero," denoting absence of A and B agglutinogens.

as a prefix in Irish names, from Ir. ó, ua (O.Ir. au) "descendant."

COLLAPSE

American Heritage

Medical Dictionary

o
The Greek letter omicron. Entries beginning with this character are alphabetized under omicron.

O ¹

The symbol for the element oxygen.

O ²
abbr.
oculus

o- abbr.
ortho- (often italic)

-o-
Used as a connective to join word elements: acidophilic.

American Heritage

Science Dictionary

O
The symbol for oxygen.

oxygen (ŏk'sĭ-jən) Pronunciation Key
Symbol O
A nonmetallic element that exists in its free form as a colorless, odorless gas and makes up about 21 percent of the Earth's atmosphere. It is the most abundant element in the Earth's crust and occurs in many compounds, including water, carbon dioxide, and iron ore. Oxygen combines with most elements, is required for combustion, and is essential for life in most organisms. Atomic number 8; atomic weight 15.9994; melting point -218.4°C; boiling point -183.0°C; gas density at 0°C 1.429 grams per liter; valence 2. See Periodic Table.

Our Living Language : In 1786, the French chemist Antoine Lavoisier coined a term for the element oxygen (oxygène in French). He used Greek words for the coinage: oxy- means "sharp," and -gen means "producing." Oxygen was called the "sharp-producing" element because it was thought to be essential for making acids. Lavoisier also coined the name of the element hydrogen, the "water-producing" element, in 1788. Soon after, in 1791, another French chemist, J. A. Chaptal, introduced the word nitrogen, the "niter-producing" element, referring to its discovery from an analysis of nitric acid.