Green’s Dictionary of Slang

1. a pornographic picture that offers both the male and female genitals.

1984

Partridge DSUE (8th edn) 333/2: since ca. 1920.

2. two prostitutes in tandem, whether hired by a single client or run by a single pimp.

1986–7		Maledicta IX 148: The compilers ought to have looked farther afield and found: […] double (pimp for more than one pro).
1997		L. Davies Candy 203: They’d done doubles together, the blonde and the brunette.

3. (N.Z. prison) a 2oz packet of prison tobacco.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 60/2: double n. 1 (also dub) a two-ounce packet of prison tobacco, formerly sold in prison canteens.