Source : Webster's Revised Unabridged Dictionary (1913)

Untie \Un*tie"\, v. t. [AS. unt?gan. See 1st {Un-}, and {Tie},
   v. t.]
   1. To loosen, as something interlaced or knotted; to
      disengage the parts of; as, to untie a knot.

            Sacharissa's captive fain Would untie his iron
            chain.                                --Waller.

            Her snakes untied, sulphurous waters drink. --Pope.

   2. To free from fastening or from restraint; to let loose; to
      unbind.

            Though you untie the winds, and let them fight
            Against the churches.                 --Shak.

            All the evils of an untied tongue we put upon the
            accounts of drunkenness.              --Jer. Taylor.

   3. To resolve; to unfold; to clear.

            They quicken sloth, perplexities untie. --Denham.

Untie \Un*tie"\, v. i.
   To become untied or loosed.

Source : WordNet®

untie
     v 1: undo the ties of; "They untied the prisoner" [syn: {unbrace},
           {unlace}] [ant: {tie}]
     2: cause to become loose; "undo the shoelace"; "untie the
        knot"; "loosen the necktie" [syn: {undo}, {loosen}]
     [also: {untying}]