Noun
sap-wood (plural sap-woods)
Alternative form of sapwood
Hence, a cross-section of a yew longbow shows the narrow, light-coloured sap-wood on the 'straight' part (riser) of the D, and the red/orange heartwood forms the curved part of the D, to balance the mechanical tension/compression stress. Source: Internet
The sap-wood is best suited to the tension on the back of the bow, and the heart-wood to the compression on the belly. Source: Internet