the.com/heartwood

means The dense, non-living wood at the core of a tree trunk, formed from old xylem cells that no longer transport sap but instead provide structural strength and often resist decay.

from A straightforward compound of 'heart' and 'wood' — English speakers simply looked at a cut log, saw the darker, denser ring at its center, and reached for the most intuitive word for 'middle of something vital.' It parallels other Germanic languages that name this layer similarly, since the logic — center equals heart — is common sense rather than borrowed imagery. The term sits opposite 'sapwood,' the pale, living outer wood still carrying sap, making the pair a tidy lesson in how trees retire their own cells into service as pure scaffolding.