The Collaborative International Dictionary of English v.0.48:

Mouser \Mous"er\, n.
   1. A cat that catches mice; as, a good mouser is better than
      a dozen mousetraps.
      [1913 Webster +PJC]

   2. One who pries about on the lookout for something.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mouser
    n 1: a cat proficient at mousing

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "mouser":
   Cheshire cat, Chinchilla cat, Maltese cat, alley cat, blue cat,
   calico cat, cat, feline, gib, gib-cat, grimalkin, house cat, kit,
   kitling, kitten, kitty, kitty-cat, puss, pussy, pussycat,
   silver cat, tabby, tabby cat, tiger cat, tom, tomcat,
   tortoise-shell cat