pronate

from WordNet (r) 3.0 (2006)

pronate
    v 1: turn the forearm or the hand so that the palm is directed
         downwards

from The Collaborative International Dictionary of English v.0.48

Pronate \Pro"nate\, a. [L. pronatus, p. p. of pronare to bend
   forward. See Prone.]
   Somewhat prone; inclined; as, pronate trees. --Kane.
   [1913 Webster]