The Collaborative International Dictionary of English v.0.48:

Putamen \Pu*ta"men\, n. [L.] (Bot.)
   The shell of a nut; the stone of a drupe fruit. See
   Endocarp.
   [1913 Webster]

WordNet (r) 3.0 (2006):

putamen
    n 1: the outer reddish part of the lenticular nucleus