See more synonyms for undo on Thesaurus.com
verb (used with object), un·did, un·done, un·do·ing.
  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.

Origin of undo

before 900; Middle English; Old English undōn; cognate with Dutch ontdoen. See un-2, do1
Related formsun·do·a·ble, adjective
Can be confusedundo undue
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for undo

Contemporary Examples of undo

Historical Examples of undo

  • 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.


    William D. Howells

British Dictionary definitions for undo


verb -does, -doing, -did or -done (mainly tr)
  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
Derived Formsundoer, 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

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