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}]
Source: WordNet® 2.0