Cambridge Dictionaries online Cambridge Dictionaries online

The most popular online dictionary and thesaurus for learners of English


English definition of “undo”


verb [T] (UNFASTEN)   /ʌnˈdu/ (present participle undoing, past tense undid  /ʌnˈdɪd/, past participle undone  /ʌnˈdʌn/)
to unfasten something that is closed or tied : He undid the top button of his shirt and loosened his tie .
(Definition of undo verb (UNFASTEN) from the Cambridge Academic Content Dictionary © Cambridge University Press)
Focus on the pronunciation of undo

Browse related topics

You are looking at an entry to do with Unfastening and opening, but you might be interested in these topics from the Opening and closing topic area:

More American English definitions for “undo”

Definitions of “undo” in other dictionaries

Word of the Day


the art and knowledge involved in preparing and eating good food

Word of the Day


Read our blog about how the English language behaves.

Learn More

New Words

Find words and meanings that have just started to be used in English, and let us know what you think of them.

Learn More