untie

from The American Heritage® Dictionary of the English Language, 5th Edition.

• intransitive verb To undo or loosen (a knot or something knotted).
• intransitive verb To free from something that binds or restrains.
• intransitive verb To straighten out (difficulties, for example); resolve.
• intransitive verb To become untied.

from The Century Dictionary.

• To undo, as a knot.
• To undo the fastenings, bands, cords, or wrappings of; loosen and remove the tyings from: as, to unlie a bundle; hence, to let or set loose; dissolve the bonds of; liberate.
• To loosen from coils or convolutions.
• To resolve; unfold; clear.
• To come untied; become loose.

from the GNU version of the Collaborative International Dictionary of English.

• transitive verb To loosen, as something interlaced or knotted; to disengage the parts of.
• transitive verb To free from fastening or from restraint; to let loose; to unbind.
• transitive verb To resolve; to unfold; to clear.
• intransitive verb To become untied or loosed.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb transitive To loosen, as something interlaced or knotted; to disengage the parts of; as, to untie a knot.
• verb transitive To free from fastening or from restraint; to let loose; to unbind.
• verb To resolve; to unfold; to clear.
• verb intransitive To become untied or loosed.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb undo the ties of
• verb cause to become loose