Sir Sydney, n. — Green’s Dictionary of Slang

Sir Sydney n.

also Sir Sidney

[ety. unknown]

a clasp-knife.

1812		Vaux Vocab. of the Flash Lang.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1834		(con. 1737–9) W.H. Ainsworth Rookwood (1857) 121: I’ll give her a taste of Sir Sydney.
1833		H. Smith Gale Middleton 1 153: I’ll just chiv sir sidney into him!