undo

American  

[uhn-doo] / ʌnˈdu /

verb (used with object)

undid, undone, undoing

1. to reverse the doing of; cause to be as if never done.

   Murder once done can never be undone.

2. to do away with; erase; efface.

   to undo the havoc done by the storm.

3. to bring to ruin or disaster; destroy.

   In the end his lies undid him.

4. to unfasten by releasing.

   to undo a gate; to undo a button.

5. to untie or loose (a knot, rope, etc.).

6. to open (a package, wrapping, etc.).

7. Archaic. to explain; interpret.

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undo British  

/ ʌnˈduː /

verb

1. (also intr) to untie, unwrap, or open or become untied, unwrapped, etc

2. to reverse the effects of

3. to cause the downfall of

4. obsolete to explain or solve

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Other Word Forms

• undoable
  adjective
• undoer
  noun

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."

Example Sentences

Regaining weight can undo many of the positive effects of weight loss, including improvements in blood sugar, blood pressure, and cholesterol levels.

From Science Daily • May 17, 2026

Cater said the forum had "caused unimaginable pain and suffering for bereaved families across the UK and beyond, and no punishment can undo that harm".

From BBC • May 13, 2026

But instead of fighting, both sides have doubled down on dueling blockades that are hard to undo without one side blinking.

From The Wall Street Journal • May 12, 2026

You may be worried that this would make it impossible for Congress to budget in advance, because taxpayers would undo its allocations.

From Slate • May 11, 2026

Here was an invitation to undo some of that, to knock down barriers where I could—mostly by encouraging people to get to know one another.

From "Becoming" by Michelle Obama

Related Words

• abolish
• annul
• destroy
• mar
• negate
• offset
• overturn
• quash
• reverse
• ruin
• shatter
• spoil
• subvert
• undermine
• wipe out
• wreck