Green’s Dictionary of Slang

stiff v.3

[stiff n.1 (1)]

1. to cause death, to kill, to murder.

[UK]D. Powis Signs of Crime 202: Stiff, to To kill.
[UK]J. Morton Lowspeak.
[Ire]P. McCabe Breakfast on Pluto 38: Stiff the whole fucking lot of them!
[UK]J. Cameron Brown Bread in Wengen [ebook] I heard someone got stiffed off a nose kiss one time.
[UK]J. Hawes Dead Long Enough 258: Styx, who could [...] have just had Harry stiffed this morning instead of talking it through.
[Scot](con. 1980s) I. Welsh Skagboys 128: Naebody likes tae see a young cunt stiffed.

2. to destroy.

[UK]Guardian G2 23 Nov. 4: Well done for stiffing a certain Jeffrey Archer.