The Collaborative International Dictionary of English v.0.48:

Omnivorous \Om*niv"o*rous\, a. [L. omnivorus; omnis all + vorate
   to eat greedily. See Voracious.]
   1. All-devouring; eating everything indiscriminately; as,
      omnivorous vanity; an omnivorous intellect.
      [1913 Webster +PJC]

   2. Specifically: (Zool.), Eating both animal and vegetable
      food.
      [1913 Webster] -- Om*niv"o*rous*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

omnivorous
    adj 1: feeding on both plants and animals [ant: carnivorous,
           herbivorous, insectivorous]