n. 心材

[ noun ]
the older inactive central wood of a tree or woody plant; usually darker and denser than the surrounding sapwood
<noun.plant>

Heartwood \Heart"wood`\ (h[aum]rt"w[oo^]d`), n.
The hard, central part of the trunk of a tree, consisting of
the old and matured wood, and usually differing in color from
the outer layers. It is technically known as {duramen}, and
distinguished from the softer {sapwood} or {alburnum}.