the GNU version of the Collaborative International Dictionary of English
n. The heartwood of an exogenous tree.
The Century Dictionary and Cyclopedia
n. In botany, the central wood or heart-wood in the trunk of an exogenous tree.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. the older inactive central wood of a tree or woody plant; usually darker and denser than the surrounding sapwood
Word Usage
"It lies next the bark, and after a course of years, sometimes many, as in the case of oaks, sometimes few, as in the case of firs, it becomes hardened and ultimately forms the duramen or heartwood."