unravel (v.)youdaoicibaDictYouDict[unravel 词源字典]
c. 1600 (transitive), from un- (2) + ravel (v.). Intransitive from 1640s. "The prefix is either reversive or intensive, according as ravel is taken to mean 'tangle' or 'untangle'" [Century Dictionary]. Related: Unravelled; unravelling; unravellment.[unravel etymology, unravel origin, 英语词源]