The Collaborative International Dictionary of English v.0.48:

Untwine \Un*twine"\, v. t. [1st pref. un- + twine.]
   To untwist; to separate, as that which is twined or twisted;
   to disentangle; to untie.
   [1913 Webster]

         It requires a long and powerful counter sympathy in a
         nation to untwine the ties of custom which bind a
         people to the established and the old.   --Sir W.
                                                  Hamilton.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Untwine \Un*twine"\, v. i.
   To become untwined. --Milton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

untwine
    v 1: undo what has been twined together; "untwine the strings"
         [ant: enlace, entwine, interlace, intertwine,
         lace, twine]