(sap) noun
1. The aqueous juices of plants, which contain and transport the materials necessary to vegetable growth.
2. Any vital fluid; vitality.
3. Sapwood.
4. Slang A foolish, stupid, or ineffectual person. [OE sœp]

(sap) v. sapped, sap·ping ν.t.
1. To weaken or destroy gradually and insidiously; enervate; exhaust.
2. To approach or undermine (an enemy fortification) by digging a sap or saps.
—v.i.
3. To dig a sap or saps; undermine an enemy fortification. See synonyms under WEAKEN.
—noun A deep, narrow trench or tunnel dug so as to approach or undermine a fortification. [<MF saper, sapper <sappe a spade <Ital. zappe <zappa a goat; with ref. to resemblance of the handle to a goat's horns]