Green’s Dictionary of Slang

to stun, to knock down; to kill.

1725		New Canting Dict. n.p.: silent to knock a Man down, so as to stun him: To lay him down for dead […].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. 1725].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: To silence a man, to knock him down, or stun him.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1859		Matsell Vocabulum 80: silence To kill; to knock down.
1882		Green-Mountain Freeman (Montpelier, VT) 31 May 2/3: The victims were [...] silenced by blow after blow, driven deep into the heart and lungs.
1895		C. Crowe Aus. Sl. Dict. 74: Silence, to kill or knock down.
1900		Marvel XIV:344 June 10: He’s been spying upon us, and must be silenced.
1905		Ukian Republic Press (CA) 1 Dec. 2/1: He [...] was silenced by blows dealt by the larger of the lads.
1911		Galveston Dly News 16 Apr. 41/6: The wretched children had slung together [...] not even daring to cry lest they should be silenced with blows.
1923		Montana Standard (Butte, MT) 9 June 1/6: [headline] Husband Slaughtered for Money and Wife Silenced by Blow on Head with Axe.
1983		C. Heath A-Team 2 (1984) 33: We scared that mick plenty. I’ll think he’ll clam up until we get around to silencing him for good.
2002		Post-Crescent (Appleton, WI) 12 Jan. 6/7: He was murdered, silenced with poison.