Green’s Dictionary of Slang

peter n.5

also pete, peter-drop

1. [late 19C+] (US tramp) drugged or adulterated liquor, derived from nitroglycerine; a ‘knockout’ drug; thus peterman, peter-thrower, a thief who uses ‘knockout drops’; pete job, any form of criminality that involves the administration of knock-out drops.

2. [1920s–30s] (UK Und.) nitroglycerine.

In compounds

peterman (n.)

[late 19C–1900s] one who uses knockout drops to facilitate a robbery.

peter player (n.) (also peter-thrower)

[mid–late 19C] (US) one who uses knockout drops to facilitate a robbery.