The Collaborative International Dictionary of English v.0.48:

Tomcat \Tom"cat`\ (t[o^]m"k[a^]t`), n. [Tom (see Tomboy) +
   cat.]
   A male cat, especially when full grown or of large size.
   [1913 Webster]

WordNet (r) 3.0 (2006):

tomcat
    n 1: male cat [syn: tom, tomcat]

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "tomcat":
   Cheshire cat, Chinchilla cat, Maltese cat, alley cat, billy,
   billy goat, blue cat, boar, bubbly-jock, buck, bull, bullock,
   calico cat, cat, chanticleer, cock, cockerel, dog, drake, entire,
   entire horse, feline, gander, gib, gib-cat, gobbler, grimalkin,
   hart, he-goat, house cat, kit, kitling, kitten, kitty, kitty-cat,
   mouser, peacock, puss, pussy, pussycat, ram, rooster, silver cat,
   stag, stallion, steer, stot, stud, studhorse, tabby, tabby cat,
   tiger cat, tom, tom turkey, top cow, top horse, tortoise-shell cat,
   tup, turkey gobbler, turkey-cock, wether