The Collaborative International Dictionary of English v.0.48:

Herbivore \Her"bi*vore\, n. [Cf. F. herbivore.] (Zool.)
   One of the Herbivora. --P. H. Gosse.
   [1913 Webster]

WordNet (r) 3.0 (2006):

herbivore
    n 1: any animal that feeds chiefly on grass and other plants;
         "horses are herbivores"; "the sauropod dinosaurs were
         apparently herbivores"

Moby Thesaurus II by Grady Ward, 1.0:

63 Moby Thesaurus words for "herbivore":
   Brillat-Savarin, Lucullus, amphibian, aquatic, biped,
   board-and-roomer, boarder, bon vivant, canine, cannibal, carnivore,
   connoisseur of food, consumer, cosmopolite, diner, diner-out,
   eater, eater-out, epicure, feeder, feline, flesh-eater, fruitarian,
   gastronome, glutton, gnawer, gourmand, gourmet, grain-eater,
   graminivore, granivore, high liver, hungry mouth, insectivore,
   invertebrate, lactovegetarian, luncher, mammal, mammalian,
   man-eater, marsupial, marsupialian, meat-eater, mouth, omnivore,
   omophagist, pantophagist, phytophage, picnicker, plant-eater,
   predacean, primate, quadruped, reptile, rodent, ruminant,
   scavenger, trencherman, ungulate, varmint, vegetarian, vermin,
   vertebrate