Source : Webster's Revised Unabridged Dictionary (1913)

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}.

Source : WordNet®

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