Source : Webster's Revised Unabridged Dictionary (1913)

Sea cow \Sea" cow`\ (Zo["o]l.)
   (a) The mantee.
   (b) The dugong.
   (c) The walrus.

Source : WordNet®

sea cow
     n : any of two families of large herbivorous aquatic mammals
         with paddle-shaped tails and flipper-like forelimbs and
         no hind limbs [syn: {sirenian mammal}, {sirenian}]