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