the.com/sapwood

means The pale, younger outer layer of wood in a tree trunk that transports water and nutrients, as opposed to the darker, dead heartwood at the core.

from Straightforward Old English compounding: 'sap,' the plant's lifeblood fluid, plus 'wood.' The word has stayed almost unchanged for centuries because it describes exactly what it names — the wood where the sap actually runs, unlike heartwood, which is older, sap-free tissue the tree has essentially retired from active duty.