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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. 2015.
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Examples from the web for undo
  • Now a small, dedicated group tries to undo some of the damage.
  • Needless to say, it has taken me a couple of days to undo that day.
  • They undo the cables, they're back in the cab, and away they go.
  • And to do it, they will have to undo all your efforts.
  • Now he set about crafting a new theory of interpretation, one that would undo prevailing principles of meaning.
  • The first is easy to detect and disdain, if difficult to undo.
  • We need to find ways, with reasonable protections, to undo that.
  • Eliminating these aggregates, scientists say, could potentially halt or undo the damage inflicted by these diseases.
  • Until then, we'll be all hands on deck trying to identify and undo the spaghetti-bowl of depleting factors in play today.
  • Progress sometimes has major constraints that are difficult to undo.
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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