drop: [OE] Drop, droop, and drip are closely related. Droop  was borrowed from Old Norse drūpa, which came from a Germanic base *drūp-. A variant of this, *drup-, produced Middle Danish drippe, the probable source of English drip , and a further variant, *drop-, lies behind Old English dropa, ancestor of modern English drop.
All three go back ultimately to a prehistoric Indo-European *dhreub-, source of Irish drucht ‘dew’. The English noun originally meant ‘globule of liquid’, and its related verb ‘fall in drops’. The main modern transitive sense, ‘allow to fall’, developed in the 14th century, giving English a single word for the concept of ‘letting fall’ not shared by, for example, French and German, which have to use phrases to express it: respectively, laisser tomber and fallen lassen. => drip, droop
Old English dropa "a drop of liquid," from Proto-Germanic *drupon (cognates: Old Saxon dropo, Old Norse dropi, Dutch drop, Old High German tropfo, German Tropfen (n.)), from PIE *dhreu-. Meaning "an act of dropping" is from 1630s; of immaterial things (prices, temperatures, etc.) from mid-19c. Meaning "lozenge, hard candy" is 1723. Meaning "secret place where things can be left illicitly and picked up later" is from 1931. Drop in the bucket (late 14c.) is from Isa. ix:15 [KJV]. At the drop of a hat "suddenly" is from 1854; drop-in "casual visit" is 1819; drop-kick is 1857. To get the drop on someone originally was Old West gunslinger slang (1869).
Old English dropian "to fall in drops" (see drop (n.)). Meaning "to fall vertically" is late 14c. Transitive sense "allow to fall" is mid-14c. Related: Dropped; dropping. Exclamation drop dead is from 1934; as an adjective meaning "stunning, excellent" it is first recorded 1970.