un·​do | \ ˌən-ˈdü How to pronounce undo (audio) , ˈən-\
undid\ ˌən-​ˈdid How to pronounce undid (audio) , ˈən-​ \; undone\ ˌən-​ˈdən How to pronounce undone (audio) , ˈən-​ \; undoing\ ˌən-​ˈdü-​iŋ How to pronounce undoing (audio) , ˈən-​ \

Definition of undo

transitive verb

1 : to open or loose by releasing a fastening
2 : to make of no effect or as if not done : make null : reverse
3a : to ruin the worldly means, reputation, or hopes of a politician undone by scandal
b : to disturb the composure of : upset she's come undone

intransitive verb

: to come open or apart

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Other Words from undo

undoer \ ˌən-​ˈdü-​ər How to pronounce undoer (audio) , ˈən-​ \ noun

Synonyms & Antonyms for undo



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Examples of undo in a Sentence

You can't undo the past. The damage cannot be undone. He was undone by greed.
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Recent Examples on the Web The rollback of the 2015 measure, known as the Waters of the United States rule, adds to a long list of environmental rules the administration has worked to weaken or undo in the past 2½ years. BostonGlobe.com, "Trump administration will repeal a key Obama-era clean water rule - The Boston Globe," 13 Sep. 2019 For starters, the NCAA would not sit by idly while California attempts to undo decades of NCAA policy. Michael Mccann, SI.com, "What Will Happen If the California 'Fair Pay to Play Act' Gets Signed Into Law?," 10 Sep. 2019 The rule proposed by Trump’s EPA would undo this whole effort, sparing companies the tedious obligation of frequent inspections and monitoring to detect methane leaks. Steve Chapman, chicagotribune.com, "Column: Trump’s EPA keeps trashing the planet," 30 Aug. 2019 Those cases involving California peace officers are detailed in documents recently made public under a landmark transparency law that undid decades of secrecy surrounding police internal affairs files. Maya Lau, latimes.com, "Destroyed files and long delays: California police slow to release misconduct records," 30 June 2019 Environmental Protection Agency Administrator Andrew Wheeler signed a final rule Wednesday that will undo Obama-era climate requirements for coal plants in a way the Trump administration insists will still reduce emissions. CBS News, "EPA Administrator Andrew Wheeler moves to roll back coal-fired power plant rules," 19 June 2019 The bad news: A Columbia University study suggests that an increase in parents smoking pot around their children could undo decades of effort to protect our kids. Sonja Haller, USA TODAY, "More parents are smoking pot around kids; children inhaling second-hand smoke," 14 May 2018 Short of undoing global warming, researchers say giant sequoias stand a much better chance of survival with better forest management. Kurtis Alexander, SFChronicle.com, "Giant sequoias — long survivors of the forest — succumbing to climate-driven wildfires," 12 Sep. 2019 The justices’ order late Wednesday temporarily undoes a lower-court ruling that had blocked the new asylum policy in some states along the southern border. Mark Sherman, The Denver Post, "Supreme Court allows nationwide enforcement of new Trump administration restrictions on asylum seekers," 11 Sep. 2019

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'undo.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of undo

before the 12th century, in the meaning defined at transitive sense 1

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Statistics for undo

Last Updated

4 Nov 2019

Time Traveler for undo

The first known use of undo was before the 12th century

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More Definitions for undo


How to pronounce undo (audio)

English Language Learners Definition of undo

: to open or release (something) : to unfasten or loosen (something)
: to change or stop the effect of (something)
formal : to cause the failure of (someone or something)


un·​do | \ ˌən-ˈdü How to pronounce undo (audio) \
undid\ -​ˈdid \; undone\ -​ˈdən \; undoing\ -​ˈdü-​iŋ \; undoes\ -​ˈdəz \

Kids Definition of undo

1 : untie sense 2, unfasten Can you undo this knot?
2 : to cancel the effect of : reverse The damage cannot be undone.
3 : to cause the ruin or failure of He was undone by greed.

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More from Merriam-Webster on undo

Thesaurus: All synonyms and antonyms for undo

Rhyming Dictionary: Words that rhyme with undo

Spanish Central: Translation of undo

Nglish: Translation of undo for Spanish Speakers

Britannica English: Translation of undo for Arabic Speakers

Comments on undo

What made you want to look up undo? Please tell us where you read or heard it (including the quote, if possible).


to engage in dissolute behavior

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