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.

1630s, "a tangle;" 1832, "a broken thread, a loose end," from ravel (v.). As the name of a weaving instrument for guiding separate yarns, 1805, also raddle, but this is perhaps a separate word influenced by ravel.

RADDLE. In New England, an instrument consisting of a wooden bar, with a row of upright pegs set in it, which is employed by domestic weavers to keep the warp of a proper width, and prevent it from becoming entangled when it is wound upon the beam of a loom. [Bartlett, "Dictionary of Americanisms," 1848]

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.

"wear off by rubbing," c. 1400, from Old French fraiier, froiier "to rub against, scrape; thrust against" (also in reference to copulation), from Latin fricare "to rub, rub down" (see friction). Intransitive sense "to ravel out" (of fabric, etc.) is from 1721. The noun meaning "a frayed place in a garment" is from 1620s. Related: Frayed; fraying.