The Collaborative International Dictionary of English v.0.48:

Aye-aye \Aye"-aye`\, n. [From the native name, prob. from its
   cry.] (Zool.)
   A singular nocturnal quadruped, allied to the lemurs, found
   in Madagascar (Cheiromys Madagascariensis), remarkable for
   its long fingers, sharp nails, and rodent-like incisor teeth.
   [1913 Webster]

WordNet (r) 3.0 (2006):

aye-aye
    n 1: nocturnal lemur with long bony fingers and rodent-like
         incisor teeth closely related to the lemurs [syn: aye-
         aye, Daubentonia madagascariensis]