The Collaborative International Dictionary of English v.0.48:

Supination \Su`pi*na"tion\, n. [L. supinare, supinatum, to bend
   or lay backward, fr. supinus supine: cf. F. supination. See
   Supine.] (Physiol.)
   (a) The act of turning the hand palm upward; also, position
       of the hand with the palm upward.
   (b) The act or state of lying with the face upward. Opposed
       to pronation.
       [1913 Webster]

WordNet (r) 3.0 (2006):

supination
    n 1: rotation of the hands and forearms so that the palms face
         upward [ant: pronation]