WordNet (r) 3.0 (2006):

varmint
    n 1: an irritating or obnoxious person [syn: vermin,
         varmint]
    2: any usually predatory wild animal considered undesirable;
       e.g., coyote [syn: varmint, varment]

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "varmint":
   amphibian, animal, aquatic, beast, biped, brute, canine, cannibal,
   carnivore, cosmopolite, creature, creeping thing, critter, cur,
   dog, dumb animal, dumb friend, feline, gnawer, herbivore, hound,
   hyena, insect, insectivore, invertebrate, living being,
   living thing, mammal, mammalian, marsupial, marsupialian, mongrel,
   omnivore, pig, polecat, primate, quadruped, reptile, rodent,
   ruminant, scavenger, serpent, skunk, snake, swine, ungulate,
   vermin, vertebrate, viper, whelp, worm