Green’s Dictionary of Slang

1. (UK Und.) a cosh, blackjack or life-preserver.

1852		Bell’s Life in Sydney 16 Oct. 1/3: I’m afeard your neddy fell heavy.
1857		‘Ducange Anglicus’ Vulgar Tongue.
1858		A. Mayhew Paved with Gold 383: His ‘neddy,’ or life-preserver, was held above their heads, ready to strike if necessary.
1860		Argus (Melbourne) 4 Feb. 6/2: The prisoner had a neddy in the first instance, and that being taken from him, he went away, and returned [...] with a tomahawk.
1865		Leaves from Diary of Celebrated Burglar 41/1: I consider it to be ‘my game’ to get out of it in the readiest way I can, and what could be readier than a ‘neddy’ just then?
1879		‘Autobiog. of a Thief’ in Macmillan’s Mag. (London) XL 503: We shall want some twirls and the stick (crowbar), and bring a neddie (life preserver) with you.
1884		Referee 21 Dec. 1/2: If husbands left off kicking their wives to death... and if the neddy and knuckle-duster went suddenly out of fashion [F&H].
1885		Ovens and Murray Advertiser (Beechworth, Vic.) 12 Sept. 4/3: I read that the English burglar no longer trusts to the silent, but lethal, ‘neddy’ to disable an officious policeman, but is now armed with the revolver.
1895		C. Crowe Aus. Sl. Dict. 52: Neddy, a life-preserver.
1896		A. Morrison Child of the Jago (1982) 184: ‘A neddy!’ Josh cut in, scornfully pointing his thumb at the instrument, which some call a life-preserver. ‘A neddy for Weech!’.
1977		D. Powis Signs of Crime 194: Neddy A cosh.

2. (US) a sling-shot.

1881

Northern Trib. (Cheboygan, MI) 5 Nov. 3/1: A slung-shot [sic] is a ‘neddy’.