Green’s Dictionary of Slang

1. (also nacker) a worn-out horse, fit only for slaughter.

1832		Mr Mathews’ Comic Annual 18: I say, aggravating Sam, vot’s the worth o’ your two knackers. Vy, that von’s vorth fifteen shillings alive, and von pound five vhen dead.
1848		Flash Dict. in Sinks of London Laid Open.
1859, 1860		Hotten Dict. of Modern Sl. etc.
1862		J.A. Hardwick ‘The Browns Ruralising’ in Prince of Wales’ Own Song Book 41: He owned a knacker – thorough-bred [...] With bony limbs and skinny head.
1878		Illus. Police News 30 Mar. 3/3: He had a knacker belonging to ‘Coper Teddy’ to sell.
1889		Dead Bird (Sydney) 20 July 2/4: A raw-boned goose-rumped knacker.
1890		Dead Bird (Sydney) 22 Mar. 7/2: A pony which can donkey lick any 14 2 knacker in N.S.W.
c.1900		T. Woottwell ‘The fces I’ve Seen’ 🎵 [H]e makes some jossey backer put his money on a nacker / That it takes a jockey all his time to jerk around the course.
1911		Truth (Perth) 25 Feb. 8/8: But me cab and quiet knacker / As i do drive of a day.

2. by ext. a worn-out, useless person.

1892

H. Nisbet Bushranger’s Sweetheart 64: He ought to be sold and salted for being such a slow old knacker.

3. (Aus.) a A$2 bill.

1967

‘Whisper All Aussie Dict.’ in Kings Cross Whisper (Sydney) xxxv 6/3: knacker: A two-dollar bill. A pound was known as a knicker and the ram showing on the two-dollar suggested the knacker.

4. (Irish) a general insult aimed at a person.

1990		R. Doyle Snapper 46: Don’t think you can stroll in and out of here when you feel like it and shout language like a – like a knacker.
2004		P. Howard PS, I Scored the Bridesmaids 205: Boggers everywhere, in their county colours, like the knackers they are.
2017		L. McInerney Blood Miracles 83: Knackers skulking through our sculpted briars, dropping fag butts, scaring the cats.

5. (Irish) a traveller, a tinker.

1996

P. Howard The Joy (2015) [ebook] [They] started exchanging a bit of rapid-fire patter, which me and Redser didn’t understand. It’s like they have their own bleedin language or something, those knackers. [Ibid.] ‘I’ve nothing against knackers, right? Live and let live, that’s my fuggin motto’.

6. (UK juv.) a thief.

2001		G. Coughlan Everyday Eng. and Sl. 🌐 Gouger (As used by Dublin Gardaí) (n): a dangerous knacker/thief.
2001		OnLine Dict. of Playground Sl. 🌐 knacker (1) n. Unwashed thieving person, often said to be found living in caravans on laybys on B-roads in Britain.