Source : Webster's Revised Unabridged Dictionary (1913)

Thunderbird \Thun"der*bird`\, n. (Zo["o]l.)
   An Australian insectivorous singing bird ({Pachycephala
   gutturalis}). The male is conspicuously marked with black and
   yellow, and has a black crescent on the breast. Called also
   {white-throated thickhead}, {orange-breasted thrust},
   {black-crowned thrush}, {guttural thrush}, and
   {black-breasted flycatcher}.

Source : WordNet®

thunderbird
     n : (mythology) the spirit of thunder and lightning believed by
         some Native Americans to take the shape of a great bird