sap

\ \ English has three distinct words sap. The oldest, ‘plant-juice’ [OE], goes back to a prehistoric Germanic *sappam, which also produced German saft ‘juice’. This in turn was a descendant of Indo-European *sapon-, from which came Latin sapa ‘new wine’. Sap ‘undermine’ [16] was borrowed via French saper from Italian zappare, which may have been ultimately of Arabic origin. Its original literal sense ‘dig a trench or tunnel underneath in order to attack’ has now been largely superseded by the metaphorical ‘weaken’, which has been heavily influenced by sap ‘plant-juice’ (from the notion of ‘draining sap from a plant’). The colloquial sap ‘fool’ [19] may be short for an earlier sapskull, a compound formed from sap in the now seldom heard sense ‘sapwood’ – hence ‘wooden head’.