Green’s Dictionary of Slang

1. a drink of alcohol.

2000

(con. 1940s–60s) Décharné Straight from the Fridge Dad.

2. (US prison) prison coffee.

1950		Goldin et al. DAUL 142/1: Mouth-wash. (P) Coffee served in the prison mess-hall.
1992		Bentley & Corbett Prison Sl. 67: Flit also Mouthwash, Spow Old term for coffee.