pollex

from WordNet (r) 3.0 (2006)

pollex
    n 1: the thick short innermost digit of the forelimb [syn:
         {thumb}, {pollex}]

from The Collaborative International Dictionary of English v.0.48

Pollex \Pol"lex\, n.; pl. {Pollices}. [the thumb.] (Anat.)
   The first, or preaxial, digit of the fore limb, corresponding
   to the hallux in the hind limb; the thumb. In birds, the
   pollex is the joint which bears the bastard wing.
   [1913 Webster]