The Collaborative International Dictionary of English v.0.48:

Untangle \Un*tan"gle\, v. t. [1st pref. un- + tangle.]
   To loose from tangles or intricacy; to disentangle; to
   resolve; as, to untangle thread.
   [1913 Webster]

         Untangle but this cruel chain.           --Prior.
   [1913 Webster]

WordNet (r) 3.0 (2006):

untangle
    v 1: release from entanglement of difficulty; "I cannot
         extricate myself from this task" [syn: extricate,
         untangle, disentangle, disencumber]
    2: become or cause to become undone by separating the fibers or
       threads of; "unravel the thread" [syn: unravel, unknot,
       unscramble, untangle, unpick] [ant: knot, ravel,
       tangle]

Moby Thesaurus II by Grady Ward, 1.0:

72 Moby Thesaurus words for "untangle":
   answer, bottom, break loose, break out, clarify, clear, clear up,
   crack, cut loose, debug, decipher, decode, disembarrass,
   disembroil, disencumber, disengage, disentangle, disintricate,
   disinvolve, dislodge, divine, do, dope, dope out, explain,
   extricate, fathom, figure out, find out, find the answer,
   find the solution, free, get, get out, get right, guess,
   guess right, have it, hit it, interpret, make out, open the lock,
   plumb, psych, psych out, puzzle out, ravel, ravel out, release,
   resolve, riddle, solve, sort out, tear loose, unbraid, unclutter,
   uncoil, undo, unknot, unlock, unmix, unravel, unriddle, unscramble,
   unsnarl, unthread, untwine, untwist, unweave, unwind, work,
   work out