The Collaborative International Dictionary of English v.0.48:

Pika \Pi"ka\, n. (Zool.)
   Any one of several species of tailless rodents of the genus
   Ochotona (formerly Lagomys), resembling small rabbits,
   but with short ears alnd legs. They inhabit the high
   mountains of Asia and America. Called also calling hare,
   and crying hare and rock rabbit. See Chief hare.
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

pika
    n 1: small short-eared burrowing mammal of rocky uplands of Asia
         and western North America [syn: pika, mouse hare, rock
         rabbit, coney, cony]