The Collaborative International Dictionary of English v.0.48:

Rodent \Ro"dent\, n. (Zool.)
   One of the Rodentia.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rodent \Ro"dent\, a. [L. rodens, -entis, p. pr. of rodere to
   gnaw. See Rase, v. t., and cf. Rostrum.]
   1. Gnawing; biting; corroding; (Med.) applied to a
      destructive variety of cancer or ulcer.
      [1913 Webster]

   2. (Zool.)
      (a) Gnawing.
      (b) Of or pertaining to the Rodentia.
          [1913 Webster]

WordNet (r) 3.0 (2006):

rodent
    n 1: relatively small placental mammals having a single pair of
         constantly growing incisor teeth specialized for gnawing
         [syn: rodent, gnawer]

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "rodent":
   amphibian, aquatic, biped, canine, cannibal, carnivore,
   cosmopolite, feline, gnawer, herbivore, insectivore, invertebrate,
   mammal, mammalian, marsupial, marsupialian, mouselike, mousy,
   omnivore, primate, quadruped, ratty, reptile, rodential, ruminant,
   scavenger, ungulate, varmint, vermin, verminous, vertebrate