Green’s Dictionary of Slang

1. a glass of beer; thus phr. with a few jars on, drunk.

1925		S. O’Casey Juno and the Paycock Act I: A wet – a jar – a boul!
1939		Rover 18 Feb. 8: ‘What about a drink as a parting toast?’ ‘Sure!’ replied Dave, ‘I’ll get the jar.’.
c.1940–5		‘Myles na gCopaleen’ Best of Myles (1968) 47: Your man is smart [...] And he doesn’t take a jar, that’s another thing that stands to him. And of course he bars the fags as well.
1954		B. Kiely Honey Seems Bitter 15: Have a jar. By Jesus we need it.
1963–74		B. Humphries Barry McKenzie [comic strip] in Complete Barry McKenzie (1988) 17: Cripes, I’ve had a real cow of a day as regards the odd ice cold jar.
1970		C. Brown Down All the Days 5: Just a few jars, that’s all – but not jarred.
1971		T. Lewis Plender [ebook] ‘I’ve got time for a quick jar’.
1982		E. Mac Thomáis Janey Mack, Me Shirt is Black 150: A fellow upstairs with a few jars on him shouted back down to the conductor.
1989		H. Leonard Out After Dark 4: They invite me out for a jar so’s people will think they’re terrible men for the women.
1997		C. McPherson The Weir 55: She does be alright on her own, with coming out for an old jar or that.
2000		Guardian G2 10 Jan. 3: Will you be having a few jars?
2009		T. Black Gutted 138: I was wondering if I could get you a pint [...] if you got the time for a quick jar.
2009		R. Milward Ten Storey Love Song 233: [A] few jars down the Golden Lion.

2. (drugs) a quantity of pills, usu. 500 or 1000 [the amount in the jars supplied to pharmacists].

1980

E. Folb Runnin’ Down Some Lines 169: Don’t hardly see no jar. Money ain’t long enough. White boy, now he kin cop a jar. He got d’ bread to buy d’ whole candy store!