- sap (n.1)
- "liquid in a plant," O.E. sæp, from P.Gmc. *sapom (cf. M.L.G., M.Du., Du. sap, O.H.G. saf, Ger. Saft "juice"), from PIE *sapon- (cf. L. sapere "to taste"), from base *sab- "juice, fluid" (cf. Skt. sabar- "sap, milk, nectar").
- sap (n.2)
- "simpleton," 1815, probably from earlier sapskull (1735), from sap as a shortened form of sapwood "soft wood between the inner bark and the heartwood," from sap (n.1) + wood, so called because it conducts the sap; cf. sappy.
- sap (v.)
- "weaken or destroy insidiously," 1755, originally "dig a trench toward the enemy's position" (1598), from M.Fr. saper, from sappe "spade," from L.L. sappa "spade" (cf. It. zappa, Sp. zapa "spade"). The sense of "weaken" probably was influenced by the verb (1725) form of sap (n.1) on the notion of "draining the vital sap from."