O
- OAP
- Old Age Pensioner (qv) (US: Senior Citizen)
- off-licence / offie
- shop licensed to sell alcoholic beverages for consumption off the premises (US equivalent: liquor store). Known in some parts of N England as "selling-out shop".
- off-the-peg
- of clothes etc., ready-made rather than made to order (US: off-the-rack)
- offal *
- the entrails and internal organs of a butchered animal.
- oi
- coarse exclamation to gain attention, roughly equivalent to "hey" ("Oi, you!" = "Hey you!")
- the Old Bill
- (slang) The police - specifically the Metropolitan Police in London, but use of the term has spread to the surrounding Home Counties.
- one-off *
- something that happens only once; limited to one occasion (as an adjective, a shared synonym is one-shot; as a noun )
- on the piss
- (vulgar) drinking heavily; going out for the purpose of drinking heavily; at a slight angle, said of an object that should be vertical
- Oriental *
- used to describe the origin of a person from East Asia (China, Japan etc.) (US:Asian - N.B. In BrE, Asian is generally reserved for people from around the Indian sub-continent: India, Pakistan, Bangladesh etc.)
- orientate *
- less common alternative to orient, deprecated by some as an unnecessary back-formation from orientation
- Other ranks
- members of the military who are not commissioned officers. (US: Enlisted ranks)
- overdraft
- money used on a bank account making a debit balance ; the amount of the debit balance, an 'overdraft facility' is permission from a bank to draw to a certain debit balance.
- overleaf *
- on the other side of the page
- owt
- anything. Northern English. "Why aren't you saying owt?" See also 'nowt' - as in the phrase "can't get owt for nowt" meaning "can't get anything for nothing."
- oy
- See "oi".
Read more about this topic: List Of British Words Not Widely Used In The United States