hackum, n. — Green’s Dictionary of Slang

hackum n.

[SE hack, i.e. he fig. hacks about him]

1. a braggart.

c.1698		B.E. Dict. Canting Crew.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Hackum, Captain Hackum; a bravo, a slasher.
1811		Lex. Balatronicum.

2. (US) one who uses a knife.

1881		Trumble Sl. Dict. (1890) 17: Hackum. Slasher with a knife.
1895		Crowe Aus. Sl. Dict. 34: Hackum, to slash with a knife.