The Collaborative International Dictionary of English v.0.48:

Spadefoot \Spade"foot`\ (sp[=a]d"f[oo^]t`), n. (Zool.)
   Any species of burrowing toads of the genus Scaphiopus,
   esp. Scaphiopus Holbrookii, of the Eastern United States;
   -- called also spade toad.
   [1913 Webster]

WordNet (r) 3.0 (2006):

spadefoot
    n 1: a burrowing toad of the northern hemisphere with a horny
         spade-like projection on each hind foot [syn: spadefoot,
         spadefoot toad]