unravel v.

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)).

1580s, "to entangle, become entwined confusedly," also "to untangle, disentangle, unwind" (originally with out), from Dutch ravelen "to tangle, fray," rafelen "to unweave," from rafel "frayed thread," which is of uncertain origin. The seemingly contradictory senses of this word (ravel and unravel are both synonyms and antonyms) might be reconciled by its roots in weaving and sewing: as threads become unwoven, they get tangled. The "entangling" meaning is the "more original" sense according to OED. From 1590s in the figurative sense of "make plain or clear;" 1610s as "make a minute and careful investigation." The intransitive sense, of fabric, "become untwisted or disjointed thread from thread" is by 1610s.