Etymology From Middle English undōn, from Old English ondōn, from Proto-West Germanic *andadōn (“to undo”), equivalent to un- + do. Cognate with West Frisian ûndwaan, ûntdwaan (“to undo; rid”), Dutch ontdoen (“to undo”).
1
To reverse the effects of an action.
Fortunately, we can undo most of the damage to the system by the war.
What's done can't be undone.
3 more examples
Pro.[…]it was a torment / To lay vpon the damn'd, which Sycorax / Could not againe vndoe ; it was mine Art, / When I arriu'd, and heard thee, that made gape / The Pyne, and let thee out.1610–1611 (date written), William Shakespeare, “The Tempest”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, →OCLC, [Act I, scene ii], page 4:
But Wigan undid their good work by conceding an avoidable second goal deep into first-half injury time.2011 October 15, Michael Da Silva, “Wigan 1 - 3 Bolton”, in BBC Sport:
And judging by how well the progressive and youth-favoured party did, many observers suspect this latest round of legal charges are a response to Future Forward's commitment to undo the legacy of military rule and undertake democratic reforms.2019 April 6, Caleb Quinley, “Thailand: Anti-military party leader faces sedition charges”, in Al Jazeera, Doha: Al Jazeera, retrieved 06 Apr 2019:
2
To unfasten.
Could you undo my buckle for me?
3
Colloquial To unfasten the clothing of (a person).
PROSTITUTE: Undo me. There's a dear.1971, Dr Jekyll and Sister Hyde (film)
4
Figuratively To impoverish or ruin, as in reputation; to cause the downfall of.
Woe is me, for I am undone!1611, The Holy Bible, […] (King James Version), London: […] Robert Barker, […], →OCLC:
Etymology From Middle English undōn, from Old English ondōn, from Proto-West Germanic *andadōn (“to undo”), equivalent to un- + do. Cognate with West Frisian ûndwaan, ûntdwaan (“to undo; rid”), Dutch ontdoen (“to undo”).
1
Computing, Engineering, Mathematics, Natural sciences, Physical sciences, Sciences An operation that reverses a previous action.