The Collaborative International Dictionary of English v.0.48:

cockatiel \cock"a*tiel\, Cockateel \Cock"a*teel\, n. (Zool.)
   A small gray and white Australian parrot (Leptolophus
   hollandicus, formerly Calopsitta Nov[ae]-Hollandi[ae])
   with a prominent crest; the male has bright yellow cheeks and
   crest, but the female has only a pale yellow in the face; --
   it is so called from its note.

   Syn: cockateel, cockatoo parrot, Nymphicus hollandicus.
        [1913 Webster + WordNet 1.5]

WordNet (r) 3.0 (2006):

cockatiel
    n 1: small grey Australian parrot with a yellow crested head
         [syn: cockateel, cockatiel, cockatoo parrot,
         Nymphicus hollandicus]