| OB | • ob n. (Historical) a halfpenny. • ob n. (Archaic) an objection. • ob n. (Genetics) the obese gene. |
| OD | • od n. (Now archaic, regional) (Euphemistic form of) God. • od n. (Archaic) An alleged force or natural power, supposed, by Carl Reichenbach and others, to produce the… • Od prop.n. An Indo-Aryan language spoken in Sindh and Punjab in Pakistan and Gujarat, Haryana, New Delhi and Rajasthan in India. |
| OE | • oe n. (Literary or poetic, rare) A small island. • oe n. A grandchild. • Oe sym. Oersted. |
| OF | • of prep. Expressing distance or motion. • of prep. Expressing separation. • of prep. Expressing origin. |
| OH | • oh interj. Expression of surprise. • oh interj. Expression of wonder, amazement, or awe. • oh interj. Expression of understanding, affirmation, recognition, or realization. |
| OI | • oi interj. Said to get someone’s attention; hey. • oi interj. An expression of surprise. • oi interj. An informal greeting, similar to hi. |
| OK | • ok adj. (Informal) Alternative letter-case form of OK. • Ok prop.n. A language family spoken in Papua New Guinea. • Ok prop.n. Alternative form of Ok. Abbreviation of Oklahoma. |
| OM | • om n. (Hinduism, Buddhism) A sacred, mystical syllable used in prayer and meditation. • om v. (Intransitive) To chant the sacred syllable om. • om interj. (Colloquial) Clipping of nom. |
| ON | • on adj. In the state of being active, functioning or operating. • on adj. Performing according to schedule; taking place. • on adj. Fitted; covering; being worn. |
| OO | • oo n. Any of four Hawaiian birds of the genus Moho, formerly classed with the honeyeaters and now believed to be extinct. • oo interj. Alternative form of ooh. • OO n. Alternative letter-case form of oo. |
| OP | • op n. (Informal) Clipping of operation. • op n. (Informal) Clipping of operator. • op n. (Internet slang, chiefly in the plural) Clipping of opinion. |
| OR | • or conj. Connects at least two alternative words, phrases, clauses, sentences, etc., each of which could make a passage true. • or conj. (Logic) An operator denoting the disjunction of two propositions or truth values. There are two forms… • or conj. Counts the elements before and after as two possibilities. |
| OS | • os n. (Anatomy) Synonym of bone. • os n. (Anatomy) An opening or entrance to a passage, particularly one at either end of the cervix, internal… • os n. An osar or esker. |
| OU | • ou n. A probably extinct species of Hawaiian honeycreeper, Psittirostra psittacea. • ou n. (South Africa, colloquial) A fellow, guy, bloke. • OU prop.n. Initialism of Open University. |
| OW | • ow interj. Synonym of ouch (“cry of pain”). • ow interj. (Music) Used for emotional emphasis. • 'ow adv. (Dialectal) Pronunciation spelling of how. |
| OX | • ox n. An adult castrated male of cattle (B. taurus), especially when used as a beast of burden. • ox n. Any bovine animal (genus Bos). A neat, a beef. • ox n. Abbreviation of oxygen. |
| OY | • oy interj. An exclamation typically expressing mild frustration or expressing feelings of uncertainty or concern. • oy interj. Alternative spelling of oi (“hey, hi, yo”). • ѹ let. Deprecated text encoding of оу. |