heartwood

noun

1. the hard central wood of the trunk of an exogenous tree; duramen.

noun

1. the central core of dark hard wood in tree trunks, consisting of nonfunctioning xylem tissue that has become blocked with resins, tannins, and oilsCompare sapwood

1. The older, nonliving central wood of a tree or woody plant, usually darker and harder than the younger sapwood. Unlike the sapwood, it no longer conducts water, and its main function is the support of the tree.