Old English sæp, probably of Germanic origin. The verb (dating from the mid 18th cent.) is often interpreted as a figurative use of the notion ‘drain the sap from’, but is derived originally from the verb sap, in the sense 'undermine'late 16th cent. (as a verb in the sense 'dig a sap or covered trench'): from French saper, from Italian zappare, from zappa 'spade, spadework', probably from Arabic sarab 'underground passage', or sabora 'probe a wound, explore'early 19th cent.: abbreviation of dialect sapskull 'person with a head like sapwood', from sap (in the sense 'sapwood') + skulllate 19th cent. (as a noun): abbreviation of sapling (from which such a club was originally made)