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[uhn-doo] /ʌnˈdu/
verb (used with object), undid, undone, undoing.
to reverse the doing of; cause to be as if never done:
Murder once done can never be undone.
to do away with; erase; efface:
to undo the havoc done by the storm.
to bring to ruin or disaster; destroy:
In the end his lies undid him.
to unfasten by releasing:
to undo a gate; to undo a button.
to untie or loose (a knot, rope, etc.).
to open (a package, wrapping, etc.).
Archaic. to explain; interpret.
Origin of undo
before 900; Middle English; Old English undōn; cognate with Dutch ontdoen. See un-2, do1
Related forms
undoable, adjective
Can be confused
undo, undue. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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Examples from the Web for undo
Contemporary Examples
Historical Examples
  • Come, captain, undo these ropes, and make up your mind quickly.

  • Come down, and undo the shop window, that I may get in that way.'

    Barnaby Rudge Charles Dickens
  • If a man can do whatever he thinks of—can he undo that which he has done?

    Now We Are Three Joe L. Hensley
  • No; but to go on as if hard work now can ever undo what years of idleness have done.

    The First Violin Jessie Fothergill
  • And, if I haply had erred, to undo the wrong, and release you.

    Poems William D. Howells
British Dictionary definitions for undo


verb (mainly transitive) -does, -doing, -did, -done
(also intransitive) to untie, unwrap, or open or become untied, unwrapped, etc
to reverse the effects of
to cause the downfall of
(obsolete) to explain or solve
Derived Forms
undoer, noun
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for undo

Old English undon "to unfasten and open" (a window or door), "to unfasten by releasing from a fixed position," from un- (2) + do (v.). The notion is of "to annul something that was done." Related: Undone; undoing.

Online Etymology Dictionary, © 2010 Douglas Harper
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