The Collaborative International Dictionary of English v.0.48:

Pinniped \Pin"ni*ped\, n. [L. pinna feather, fin + pes, pedis, a
   foot: cf. F. pinnip[`e]de.] (Zool.)
   (a) One of the Pinnipedia; a seal.
   (b) One of the Pinnipedes.
       [1913 Webster]

WordNet (r) 3.0 (2006):

pinniped
    n 1: aquatic carnivorous mammal having a streamlined body
         specialized for swimming with limbs modified as flippers
         [syn: pinniped mammal, pinniped, pinnatiped]