Green’s Dictionary of Slang

1. (drugs) one kilo of marijuana, hashish or any other drug.

1968		N. von Hoffman We are the People Our Parents Warned Us Against 37: Grass is available in five-hundred-kilogram lots [...] or ‘key’. [Ibid.] 171: I saw sixteen keys of grass under the bed.
1969		R.R. Lingeman Drugs from A to Z (1970) 135: key, also spelled ki. A kilogram (2.2 pounds) of a drug, especially a pressed block of marijuana of this weight.
1971		E.E. Landy Underground Dict. (1972) 114: kee [...] 2.2 pounds of marijuana.
1971		R. Woodley Dealer 10: [of cocaine][C]ocaine is sold cut in $10 or $20 capsules [...] teaspoons and tablespoons (tablespoons are ‘quarters’); ‘pieces,’ which are four tablespoons, or about an ounce; parts of ‘keys’ (kilograms, 2.2 pounds) from eighths, quarters, halves, all the way to whole keys of pure cocaine.
1971		Thom Gunn ‘Street Song’ in Moly With Midday Mick man you can’t lose, / I’ll get you anything you need. / Keys lids acid and speed.
1974		V.E. Smith Jones Men 17: He gettin’ in some keyes, you know.
1978		R.D. Pharr Giveadamn Brown (1997) 177: ‘We need thirty keys of heroin for bait’.
1980		E. Folb Runnin’ Down Some Lines 170: Next time, I’ma get me a whole fuckin’ key.
1992		V. Headley Yardie 12: Skeets seh is one ki you bring.
1992		T. Williams Crackhouse 74: Even the big-time coke man [...] even the one selling keys is selling cooked-up stuff more.
1992		UGK ‘Cocaine in the Back of the Ride’ 🎵 Sellin fifty dollar slabs as I’m slangin them ki’s.
1996		UGK ‘Hi Life’ 🎵 But I got one foot in the street / And every week I flip a Ki.
2000		W. Shaw Westsiders 11: A key is a kilo of cocaine.
2003		J. Lethem Fortress of Solitude 362: He and I and Mathew had spent the waning hours of that first afternoon divvying Arthur’s quarter kee into Camden-sized portions.
2004		T.I. ‘Long Live Da Game’ 🎵 Grab my scale / Get another ki and I'mma slang my yayo.
2013		K. Sampson Killing Pool 59: Getting the gear [i.e. cocaine] in, getting it cut and getting it back out to the network, the ten-key men, the five-key men, right down to the little street teams.
2017		D. Winslow The Force [ebook] ‘A dope case, a quarter key of coke’.
2021		Breen & Conlon Hitmen 221: ‘I made a good bit [...] on five keys [i.e. of crack cocaine]’.

2. £1000.

2000

J.J. Connolly Layer Cake 159: Would Jimmy give him two key in readies on the old man’s behalf?