From WordNet (r) 3.0 (2006) [wn]:
seahorse
n 1: either of two large northern marine mammals having ivory
tusks and tough hide over thick blubber [syn: walrus,
seahorse, sea horse]
2: small fish with horse-like heads bent sharply downward and
curled tails; swim in upright position [syn: seahorse, {sea
horse}]