What does "knacker" mean?

Knacker: One of two or more pieces of bone or wood held loosely between the fingers, and struck together by moving the hand; -- called also clapper. Halliwell.

Additional senses

  1. 2.a harness maker. [Obs. or Prov. Eng.] Halliwell.
  2. 3.One who slaughters worn-out horses and sells their flesh for dog's meat. [Eng.]

Sources