The Collaborative International Dictionary of English v.0.48:

Quittor \Quit"tor\ (kw[i^]t"t[~e]r), n. [Perhaps for quitture.]
   (Far.)
   A chronic abscess, or fistula of the coronet, in a horse's
   foot, resulting from inflammation of the tissues investing
   the coffin bone.
   [1913 Webster]