From Longman Dictionary of Contemporary Englishuntieun‧tie /ʌnˈtaɪ/ verb (untied, untying, unties) [transitive] FASTEN/DO UPto take the knots out of something, or unfasten something that has been tied OPP tie up Peter untied his shoelaces.→ See Verb table
Examples from the Corpus
untie• They asked that their wrists be untied.• He untied Dobbs and led her into a large dark shed.• Amy untied her apron and folded it neatly.• He untied his right shoe first.• It was several hours before anyone found me and untied me.• Someone had untied the boat and it had floated away.• I learned how to untie the rope and would push my brother over this picket fence.• They untie their Nikes; they cut the tape from their ankles; they shed their jerseys and put on sweatshirts.• She untied then retied the belt with nervous fingers, not quite sure what to do next. 