undo

verb

un·​do ˌən-ˈdü 

ˈən-

undid ˌən-ˈdid 

ˈən-

; undone ˌən-ˈdən 

ˈən-

; undoing ˌən-ˈdü-iŋ 

ˈən-

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

3

a

: 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

c

: seduce sense 3

intransitive verb

: to come open or apart

undoer

ˌən-ˈdü-ər 

ˈən-

noun

Synonyms

• demoralize
• emasculate
• paralyze
• unman
• unnerve
• unstring

Examples of undo in a Sentence

You can't undo the past.

The damage cannot be undone.

He was undone by greed.

Recent Examples on the Web

And once made, the alternate valuation date election cannot be undone. State Estate Taxes. —Ashley Case, Forbes, 26 Dec. 2024

For the better part of the last 63 years, the NFL has steered clear of scheduling Saturday games while school is in session, only to watch in bemusement as college football’s expansionist impulses have undone a lifetime of studied avoidance. —Anthony Crupi, Sportico.com, 20 Dec. 2024

Before the next congressional term, Republicans must undo recent unilateral moves by Biden’s IRS that would subject millions of Americans to double taxation. —Carol Miller, National Review, 16 Dec. 2024

Trump’s nascent plan to levy new tariffs on Canada and Mexico threatens to undo the U.S.-Mexico-Canada Agreement. —Allison Carnegie, Foreign Affairs, 24 Dec. 2024

Word History

First Known Use

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

Kids Definition

undo

verb

un·​do ˌən-ˈdü 

ˈən-

undid -ˈdid  ; undone -ˈdən  ; undoing -ˈdü-iŋ 

1

: to make or become unfastened or loosened : open, untie

undo a knot

2

: to destroy the effect of : nullify, reverse

3

a

: to cause the ruin of

your stubbornness undid you

undone by greed

b

: to disturb the calmness of : upset

she's come undone

undoer noun