prefix of reversal, deprivation, or removal (as in unhand, undo, unbutton), Old English on-, un-, from Proto-Germanic *andi- (source also of Old Saxon ant-, Old Norse and-, Dutch ont-, Old High German ant-, German ent-, Gothic and- "against"), from PIE *anti "facing opposite, near, in front of, before, against" (from PIE root *ant- "front, forehead," with derivatives meaning "in front of, before").
More or less confused with un- (1) through similarity in the notions of "negation" and "reversal;" an adjective such as unlocked might represent "not locked" (un- (1)) or the past tense of unlock (un- (2)).
furl v.
1550s, of uncertain origin, possibly from French ferler "to furl," from Old French ferliier "chain, tie up, lock away," perhaps from fer "firm" (from Latin firmus; from PIE root *dher- "to hold firmly, support") + -lier "to bind" (from Latin ligare; from PIE root *leig- "to tie, bind"). Also said to be a shortening of earlier furdle "to furl or fold." Related: Furled; furling. As a noun from 1640s.