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
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.
Appeared in the April 9, 2026, print edition as 'Truce Can’t Undo Region’s Energy Hangover'.
From The Wall Street Journal • Apr. 8, 2026
Undo the tight, slicked back bun and bring in halo dyed hair, dark eyeliner and the piercing she did herself on the inside of her upper lip.
From Los Angeles Times • Feb. 5, 2026
Grid View You can stop an email before it is sent by hitting Undo.
From The Verge • Sep. 10, 2022
From now on, after you send an email, you’ll see "Message sent" and the option to "Undo" or "View message" in the bottom left corner of your screen.
From Fox News • Jul. 31, 2021
Father said they are showing everybody Congolese, like Tata Undo, that Belgium is still calling the shots.
From "The Poisonwood Bible" by Barbara Kingsolver
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.
