The Collaborative International Dictionary of English v.0.48:

Grimalkin \Gri*mal"kin\, n. [For graymalkin; gray + malkin.]
   1. An old cat, especially a she-cat. --J. Philips.
      [1913 Webster]

   2. A bad-tempered old woman.
      [PJC]

Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "grimalkin":
   Cheshire cat, Chinchilla cat, Jezebel, Maltese cat, alley cat,
   beldam, bitch-kitty, blue cat, calico cat, cat, feline, fury, gib,
   gib-cat, hag, hellcat, hellhag, house cat, kit, kitling, kitten,
   kitty, kitty-cat, mouser, puss, pussy, pussycat, she-devil,
   she-wolf, silver cat, siren, tabby, tabby cat, termagant,
   tiger cat, tigress, tom, tomcat, tortoise-shell cat, virago, vixen,
   wildcat, witch