One of two or more pieces of bone or wood held loosely between the fingers, and struck together by moving the hand.
A Bachanalian dancing the Spanish Morisco, with knackers at his fingers.1649, William Cavendish, 1st Duke of Newcastle, The Variety:
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Archaic A harnessmaker or saddlemaker; their place of business (e.g., saddlery).
Plow-wright , Cart-wright, Knacker and Smith1707, J[ohn] Mortimer, The Whole Art of Husbandry; or, The Way of Managing and Improving of Land. […], London: […] J[ohn] H[umphreys] for H[enry] Mortlock […], and J[onathan] Robinson […], →OCLC:
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One who slaughters and (especially) renders worn-out livestock (especially horses) and sells their flesh, bones and hides.
Near-synonyms: slaughterer, slaughterman
After a few years even the whip loses its virtue, and the pony goes to the knacker.1933 January 9, George Orwell [pseudonym; Eric Arthur Blair], chapter XXII, in Down and Out in Paris and London, London: Victor Gollancz […], →OCLC:
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One who dismantles old ships, houses, etc. and sells their components.
Near-synonyms: salvager, salvor; scrapper, wrecker, breaker; shipbreaker, car breaker
He looked like someone had put a 9mm full metal jacket round through his left scrotum. He even had his mouth open in some parody of a soundless scream, much as I imagined I would do if someone shot my left knacker off.2013, Perry Gamsby, Never Be Unsaid, page 136:
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An old, worn-out horse.
Believe me, you can get an old knacker for cheap at the glue yard, but it won't carry you as far as a thoroughbred!2014, K. Bannerman, Mark of the Magpie, page 170: