Green’s Dictionary of Slang

(UK black/gang) a knife, thus as v. to stab.

2011		Urban Dict. 4 July 🌐 a slang term for a knife.
2018		Unknown T ‘Homerton B’ 🎵 Bandits and figures, rappers and drillers / Grab a few nanks, or grab a spare spinner.
2018-20		T. Thorne (ed.) ‘Drill Slang Glossary’ at Forensic Linguistic Databank 🌐 Nank - knife, stab.