Source : Webster's Revised Unabridged Dictionary (1913)

Duramen \Du*ra"men\, n. [L., hardness, a hardened, i. e.,
   ligneous, vine branch, fr. durare to harden. See {Dure}.]
   (Bot.)
   The heartwood of an exogenous tree.

Source : WordNet®

duramen
     n : the older inactive central wood of a tree or woody plant;
         usually darker and denser than the surrounding sapwood
         [syn: {heartwood}]