Green’s Dictionary of Slang

(a) a 28g (1oz) packet of a powdered drug.

1934		J.L. Kuethe ‘Prison Parlance’ in AS IX:1 26: cadillac. An ounce of dope.
1939		Howsley Argot: Dict. of Und. Sl.
1950		Goldin et al. DAUL 39/1: Cadillac. A one-ounce package of any of the white powdered drugs.
1960, 1975		Wentworth & Flexner DAS.
1989		J. Morton Lowspeak 34: Cadillac – an ounce of heroin, or, less usually, cocaine.
2001		ONDCP Street Terms 5: Cad/Cadillac — 1 ounce.

(b) any powdered, thus usu. narcotic, drug.

1953		Anslinger & Tompkins Traffic In Narcotics 306: a Cadillac. Cocaine.
1959		J.E. Schmidt Narcotics Lingo and Lore 24: Cadillac – A dose of a narcotic enough for one binge. Cadillac – A top quality narcotic.
2001		ONDCP Street Terms 5: Cadillac — Cocaine.

(c) phencyclidine.

1977		L. Young et al. Recreational Drugs.
1979		H. Feldman et al. Angel Dust 124: The large number of street names it has been accorded over the years: [...] cadillac.
1981		D.E. Miller Bk of Jargon 337: Cadillac: PCP.
2001		ONDCP Street Terms 5: Cadillac — PCP.

(a) coffee with cream and sugar.

1985		‘Jennifer Blowdryer’ Modern English 57: cadillac (n): Coffee with cream and lots of sugar. Helps prolong heroin high.
2000		Other Side of the Wall: Prisoner’s Dict. July 🌐 Cadillac: (1) Coffee with cream & sugar, smooth, rich and creamy.

(b) (also car) a line used for transferring articles, e.g. a pack of cigarettes, from one cell to another.

1992		Bentley & Corbett Prison Sl. 14: Car also Cadillac In ‘lockup’ units [...] inmates devise ingenious methods for passing cigarettes and other items from cell to cell. One of the most popular ways is to make a car or cadillac. A car is made by tearing bed sheets into long, narrow strips approximately three inches in width. These sheet strips are then tied to one another making one long strip. On one end is tied a paperback book which is actually referred to as the car. The book or car is then thrown to other cells, the item needed is tied to the book and the car is retrieved by pulling in the sheet strip.
2002		J. Lerner You Got Nothing Coming 76: Kansas makes a slipknot in the string, then takes a few test swings [...] before flinging the soap in a tight arc under the door. A second later Big Bear [...] has the soap/slipknot end of the Cadillac while Kansas still holds on to his end of the string.

(c) an easy job within the prison.

2000

Other Side of the Wall: Prisoner’s Dict. July 🌐 Cadillac: [...] (3) A cushion job on the inside.

(d) (also Cadillacker) something considered the best.

2000		Other Side of the Wall: Prisoner’s Dict. July 🌐 Cadillac: [...] (4) The best.
2007		UGK ‘Gravy’ 🎵 I fuck the snow but I love a pro like flatbackers I’m a Cadillac’er.

(e) a vacant cell.

2000

Other Side of the Wall: Prisoner’s Dict. July 🌐 Cadillac: [...] (5) An officer’s term for a vacant cell.

(f) (N.Z. prison) a large rectum useful for concealing large amounts of contraband.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 36/1: Cadillac, the n. 1 a spacious rectum that is well-equipped to conceal a sizeable amount of contraband.