A dictionary of slang - "O" - Slang and colloquialisms of the UK.

oats	Noun. 1. Sperm, with regard to being seeds. Used in phrases such as sow one's oats, which essentially alludes to procreation but at its most basic to having to sexual intercourse. 2. Sex. The informal phrase get ones oats meaning to have sex. E.g."You look a bit happy! Did you get your oats last night?"
odd-fish	Noun. An eccentric or unusual person.
odds	Noun. Loose change. Probably short for odds and sods. [Merseyside use]
odds and sods	Noun. Bits and pieces, miscellaneous items.
offer someone out	Vrb phrs. To challenge someone to a fight.
off it	Phrs. See 'off one's head'.
off one's box	Phrs. 1. Intoxicated by drugs or alcohol. E.g."I was so off my box last night that when my brother walked in the room I didn't recognise him." Cf. 'out of one's box'. 2. Out of one's mind, crazy.
off one's chump	Phrs. 1. Very intoxicated, by alcohol or drugs. 2. Insane, crazy. See 'chump'. E.g."He's off his chump if he thinks I'm going to let him run off with my wife!"
off one's face	Phrs. Very intoxicated by alcohol or drugs. Cf. 'out of one's face'.
off one's head	Phrs. 1. Insane, mad. 2. To be extremely intoxicated by alcohol or drugs.
off one's rocker	Phrs. Insane, crazy.
off one's tits	Phrs. Very drunk or intoxicated with drugs.
off one's tree	Phrs. 1. Insane, mad. 2. To be extremely intoxicated by alcohol or drugs.
off one's trolley	Phrs. 1. Crazy, insane. Late 1800s. [Orig. U.S.] 2. Very intoxicated.
off the hook	Phrs. Exceptionally good, cool, wonderful.
offy	Noun. A shop that sells alcohol. An abbreviated form of off licence. Also spelt offie.
oggin	Noun. 1. Sea. [Navy use] 2. Water. [Navy use]
Oh my giddy aunt!	Exclam. A mild exclamation of surprise.
...oholic	Suffix. A suffix added to emphasise the nature of a person with regard to one of their obsessive or compulsive qualities, taken from the commonly used alcoholic. Terms such as chocoholic and sexoholic are frequently heard. E.g."It's pointless calling for Jim before midday, he's a sleepoholic."
oik	Noun. An unsophisticated, uncultured and objectionable person. Derog.
oil painting	Noun. An attractive thing. Usually in the negative as 'no oil painting'. See 'no oil painting'.
oily	Noun. A cigarette. From the rhyming slang 'oily rag', meaning 'fag'.
oi oi savaloy !	Exclam. 1. A greeting or attention seeking exclamation. Cockney? [Mainly London use] 2. Used to get attention. [Mainly London use]
o.j.	Noun. Abb. of orange juice. [Orig. U.S.]
old bag	Noun. An disagreeable, elderly woman. Derog.
old banger	Noun. A delapidated old car.
old bean	Noun. A form of address. E.g."Hello old bean, how are you today?"
(the) old bill	Noun. The police. Often shortened to 'the bill'. [1950s]
old boiler	Noun. 1. An unnattractive woman. Derog. 2. Wife. Derog.
old boot	Noun. An objectionable, aging, unattractive woman. See 'boot'. Derog.
old chap	Noun. Affectionate term for one's penis. Cf 'old fellow', 'old man', 'lad'.
old cock	Noun. Affectionate term of address for a man. Also 'old cocker'.
old cocker	Noun. A form of address, usually for a man. Occasionally shortened to 'cocker'.
old fart	Noun. An elderly, old fashioned and tedious person. Derog. See 'fart'.
old fellow	Noun. Affectionate term for one's penis. Cf 'old chap', 'old man', 'lad'.
old fruit	Noun. A term of address.
old hat	Adj. Old fashioned.
old lady	Noun. Mother, girlfriend or wife.
old man	Noun. 1. Father, boyfriend or husband. 2. Affectionate term for one's penis. Cf 'old chap', 'old fellow', 'lad'.
Oliver (Twist)	Noun. Fist. Rhyming slang. E.g."Put up your Olivers and let's sort this once and for all." Adj. Drunk. Rhyming slang for 'pissed'. See 'pissed'.
on	Adj. Euphemism for the menstrual cycle. E.g."No! I don't want sex tonight, I'm on. OK?"
on a mission	Phrs. Seeking a good time.
on a promise	Phrs. To have been promised sexual intercourse by someone, usually one's partner.
once-over	Noun. An inspection, a quick look over something or someone. E.g. "I was giving it the once over when the phone rang."
one-eyed trouser-snake	Noun. The penis. Often shortened to 'trouser snake'.
one for the road	Noun. A final alcoholic drink before setting off on one's journey.
one in the departure lounge	Noun. In need of an act of defecation. E.g."Stop the car! I need the toilet, I've got one in the departure lounge."
one-night stand	Noun. A brief sexual fling.
one-off	Adj. Occurring only once. E.g."This is a one-off model, a concept car made by the same team who designed the Lotus Elite." Noun. A singular occurrence of an activity, or production of a thing. E.g."This party is a one-off, as we can't afford to have another one this year."
one over the eight	Phrs. Drunk, intoxicated by alcohol. E.g."Can someone get a taxi for Alex, he's had one over the eight and needs to go home now."
one sandwich short of a picnic	Phrs. Eccentric, insane, odd. Also as two sandwiches short of a picnic.
...one's tits off	Phrs. An addition to certain verbs to add emphasis. E.g."I laughed my tits off when I saw his new haircut, it was ridiculous!"
on one	Phrs. Acting in a slightly crazed way. E.g."I'm going home. Andy's on one and he's annoying me."
on one's billy (tod)	Phrs. On one's own. E.g."He was like an excited puppy when I visited, having spent the whole weekend on his billy tod."
on one's Jack	Phrs. Alone. Rhyming slang from Jack Jones. See 'Jack (Jones)'.
on one's tod	Phrs. Alone. Rhyming slang from Tod Sloan, the name of an American jockey.
on the batter	Phrs. Drinking alcohol, or having a drinking session. [Orig. Irish?]
on the blink	Phrs. Of machinery, or technology, not working efficiently or temporarily out of order.
on the blob	Phrs. Menstruating.
on the broo	Phrs. Unemployed, claiming unemployment benefits. Also on the burroo. [Scottish use]
on the cadge	Phrs. Begging. {Informal}
on the dole	Phrs. Receiving social security benefits. {Informal}
on the drip	Phrs. Paying by installments, on hire purchase. Cf. 'on the never never'.
on the fiddle	Phrs. In the process of cheating, or defrauding. See 'fiddle'.
on the game	Phrs. Working as a prostitute. [Mid 1900s]
on the hit	Phrs. Getting drunk. Abb. of 'on the hit and miss', rhyming slang for 'on the piss'.
on the hobble	Phrs. Working without declaring one's income when in receipt of social benefits. [South Wales use]
on the hoy	Phrs. Out getting drunk with friends. [North-east use]
on the job	Phrs. Having sexual intercourse.
on the lash	Phrs. Out getting drunk. E.g."We're on the lash tonight lads, so bring plenty of cash."
on the never never	Phrs. Paying by installments, on hire purchase. Cf. 'on the drip'.
on the Pat and Mick	Phrs. Taking time off work due to sickness. Rhyming slang for on the sick. See 'Pat and Mick'.
on the piss	Phrs. Getting drunk. E.g."He's got a hangover after going out on the piss last night."
on the pull	Phrs. Seeking a partner for sexual intimacies. E.g." We're off on the pull tonight, so have a bath and wear your best suit."
on the Q.T.	Phrs. On the quiet, secretly.
on the rag	Phrs. Menstruating.
on the razz / razzle	Phrs. Indulging in alcohol, partying, generally having a good time. A shortening of on the razzle-dazzle. E.g."I'm buying a new shirt; we're off out on the razzle tonight."
on the rob	Phrs. The act of thieving. E.g."You don't want to employ him! He's just like his older brother, always on the rob."
on the scrounge	Phrs. Seeking to obtain something at the expense of or through the generosity of others. E.g."Keep out of the way of Steve, he's on the scrounge for some cash." {Informal}
on the take	Phrs. Open to bribery, receiving bribes.
on the tap	Phrs. Meaning the same as 'on the pull'. See also 'tap off'.
on the wagon	Phrs. Teetotal, abstaining from alcohol.
on your bike!	Exclam. Go away!
oojah	Noun. A 'what's its name ?', a thing whose name has been forgotten. Often extended with other humorous additions, e.g. "An oojah ma bob", or "An oojah ma thingy."
oose	Noun. Fluff. [Scottish use]
order of the boot	Noun. Dismissal. E.g."I can't afford to go out tonight, my boss gave me the order of the boot yesterday."
oscar	Adv. Later. Rhyming slang on Oscar Slater. [Glasgow use]
O.T.T.	Phrs. Abb. of Over The Top, meaning excessive, beyond that which is acceptable.
our kid	Noun. 1. One's younger brother or sister. {Informal} 2. Affectionate term for a friend. {Informal}
out	Adj. Openly living as a homosexual. See 'closet.' Verb. To declare publicly the homosexuality of someone. Very popular direct-action of the 'Gay' community in the 1990s, in an attempt to bring a higher profile to homosexuality.
out of it	Phrs. Very intoxicated with alcohol or drugs.
out of one's head	Phrs. 1. Mad, crazy. 2. Intoxicated by alcohol or drugs. Cf. 'off one's head'.
out of one's box /tree	Phrs. See 'off of one's box'.
out of order	Adj. Of a person or their behaviour, unfair, unacceptable, or wrong. E.g."Did you see that girl screaming at her mum in the church? She was well out of order."
out of puff	Phrs. Out of breath. {Informal}
out on one's arse	Phrs. Thrown out, discarded without further consideration. E.g."Any more noise during the ballet performance and you'll all be out on your arse."
out on the town	Phrs. An evening indulging in the nightlife of a town or city. {Informal}
outtie	Noun. A navel, belly button, that protrudes. Cf. 'innie'.
out to lunch	Phrs. A euphemism for insane, or crazy. {Informal}
over my dead body!	Exclam. There is no way that I will let that happen! An emphatic rejection.
over the shoulder boulder holder	Noun. A brassiere, bra. Jocular usage. Cf. 'boulder holder'.
over the top	Phrs. Extremely exaggerated, outrageous, beyond a joke. Cf. O.T.T. {Informal}
ow do!	Exclam. Hello! How do you do! [Northern use]
owt	Pron. Anything. E.g."Is there owt on TV worth watching?" [Northern dialect]
oxo (cube)	Noun. The London underground transport system. Rhyming slang on the underground's common name, the Tube. [London use]
oxygen thief	Noun. An elderly person. Derog.