1. [n]  someone who buys up old horses for slaughter
2. [n]  someone who buys old buildings or ships and breaks them up to recover the materials in them

KNACKER is a 7 letter word that starts with K.

1. \Knack"er\, n.
   1. One who makes knickknacks, toys, etc. --Mortimer.
   
   2. 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.
   
   

2. \Knack"er\, n. [Cf. Icel. hnakkr a saddle.]
   1. a harness maker. [Obs. or Prov. Eng.] --Halliwell.
   
   2. One who slaughters worn-out horses and sells their flesh
      for dog's meat. [Eng.]