undo
Americanverb (used with object)
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to reverse the doing of; cause to be as if never done.
Murder once done can never be undone.
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to do away with; erase; efface.
to undo the havoc done by the storm.
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to bring to ruin or disaster; destroy.
In the end his lies undid him.
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to unfasten by releasing.
to undo a gate; to undo a button.
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to untie or loose (a knot, rope, etc.).
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to open (a package, wrapping, etc.).
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Archaic. to explain; interpret.
verb
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(also intr) to untie, unwrap, or open or become untied, unwrapped, etc
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to reverse the effects of
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to cause the downfall of
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obsolete to explain or solve
Other Word Forms
Derived Forms
Conjugated Forms
Present
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has undoneperfect 3rd person singular
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have undoneperfect
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have been undoingperfect progressive
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am undoingprogressive 1st person singular
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has been undoingperfect progressive 3rd person singular
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is undoingprogressive 3rd person singular
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are undoingprogressive
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undoingparticiple
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undoessingular 3rd person
Past
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had undoneperfect
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had been undoingperfect progressive
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were undoingprogressive plural
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undidsimple
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was undoingprogressive singular
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undoneparticiple
Future
Etymology
Origin of undo
First recorded before 900; Middle English; Old English undōn; cognate with Dutch ontdoen; see origin at un- 2, do 1
Explanation
When you undo something, you make it invalid, like when governments undo treaties they've signed in the past. Another way to undo is simply to open: "I couldn't undo the knot on my sneakers, so I just slipped them off." When we undo something, we cancel out its results, or reverse them. You might try to undo the damage caused by your little sister's baseball, offering to replace your neighbor's broken window. Formally, this verb also means "cause downfall or ruin," so you could say, "His love of power will undo him in the end."
Vocabulary lists containing undo
Commonly Confused Words, List 3
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Commonly Confused Words, List 5
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Commonly Confused Words, List 11
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
And it is black-letter constitutional law that the executive cannot undo such judgments.
From Slate • May 26, 2026
While creditors cannot make claims on an irrevocable trust, JDKatz adds that the court could undo your transfer to a trust.
From MarketWatch • May 23, 2026
Musk’s lawsuit is an existential threat to that relationship as he seeks to wind OpenAI back to its 2015 nonprofit roots—as well as undo its special relationship with Microsoft.
From Barron's • May 15, 2026
Nathan Hochman had said the plea marked a “step toward justice and a measure of closure for the victims,” adding that it could not undo the devastation of that day.
From Los Angeles Times • May 8, 2026
Otto ran to undo the other end so they could bind the rubbery menace and get some answers.
From "The Last Last-Day-of-Summer" by Lamar Giles
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
