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

yack (!)	Exclam. An exclamation of disgust. A variation on 'yuck!'. Verb. To talk incessantly and boringly. Also spelt yak and often extended to yack on, meaning the same.
yack up	Verb. To vomit. E.g."That was the worst meal ever; I feel like yacking up."
yacky	Adj. Disgusting, vile.
yam	Noun. Home. Also 'yem'. [North-east/Cumbrian use. Dialect?]
yampy	Adj. Crazy, mad, insane. [Birmingham/ W. Midlands use]
yam yam	Noun. A person from the Black Country, an area of England encompassing Wolverhampton, Dudley, and Stourbridge. From the way in which people from this locality speak. Derog. [Birmingham use]
yank	Noun. An act of masturbation. Male usage. E.g."Oh God! I just walked in on Martin having a yank." Verb. To masturbate. E.g."He looks like he's been up all night yanking."
yap	Verb. To talk incessantly. {Informal}
yard	Noun. One's home. [London use]
yardie	Noun. A member of a Jamaican criminal gang. Usually operating internationally and in the distribution of illicit drugs. [Jamaica]
ya wank	Noun. A contemptible person. [Scottish use]
yawn	Noun. Something that is very boring. E.g."Amanda's boyfriend is obsessed with football, he's such a yawn." {Informal}
y-bone steak	Noun. The female genitals.
yellow belly	Noun. A person from Lincolnshire.
yem	Noun. See 'yam'.
yikes!	Exclam. An expression of surprise or astonishment.
yitney	Noun. A coward. Also yitni. [Notts. & Leics. use/Dialect?]
yo!	Exclam. A greeting or an attention seeking call. [Orig. U.S.]
yob	Noun. A lout or hooligan. Derived from the backslang of boy.
yobbo	Noun. Meaning the same as 'yob'.
yomp	Verb. To walk hard and with vigour. [1900s]
yonks	Noun. An age, a long time.
you're having a laugh (!)	Phrs./Exclam. See 'having a laugh'.
yoursen	Pron. Yourself. [Northern use/Dialect]
yo-yo knickers	Noun. A promiscuous woman, a sexually loose woman. From the frequency of her underwear going up and down. Derog.
yuck (!)	Noun. A thing that is vile or distasteful. E.g."Don't eat that, it's yuck and tastes mouldy." Exclam. Expressing extreme distaste.
yucky	Adj. Very unpleasant or distasteful.