Synonyms for Undo:

adj.

loose (adjective)
disengage.

n.

unhitch, archive, browse, capture, burn, author, burn-in, block, call up, back up, access. overthrow, revise, ruin, alter, change, turn into, modify, wreck, convert, reverse, mar, make into, upset, subvert, transform, vary, unsettle, injure. expunge, scratch, strike, blot, come off, steam open, erase, vacate, continue, rub, detach, wipe, unhook, uncoil, uncouple, unroll, unfurl, cross. tighten, unloose, disengage, slip, unclasp, unfasten, unbind, unloosen. Unclose. enervate, devitalize, attenuate, strong, enfeeble, sap, debilitate, undermine, weaken, unnerve. debauch, seduce. undo (noun)
unmake, untie, unwrap, loosen.

v.

annul (verb)
dismiss, eliminate, cancel, delete, withdraw, disavow, abolish, revoke, dissolve, negate, eradicate, invalidate, veto, deny, neutralize, refute, extinguish, annul, disclaim, retract, destroy, efface, nullify, Disaffirm, reject, repudiate, divorce, abnegate, obliterate.
nullify, invalidate (verb)
negate, injure, subvert, spoil, overthrow, unsettle, neutralize, ruin, undermine, reverse, annul, destroy, wreck, cancel, mar, upset, wrack, abolish, demolish, shatter, smash.
open (verb)
release, unloose, unseal, bare, unwrap, unlock, unplug, disclose, unloosen, unfasten, unbind, loosen, uncork, untie, reveal, disengage, expose, open, Unclose.

Other synonyms:

uncoil, unclasp, attenuate, unloosen, unhook, unloose, devitalize, unroll, steam open, Unclose. enfeeble, unnerve, debilitate, torpedo, unfasten, enervate, expunge. detach, demolish, bankrupt, seduce, erase, scratch, debauch, shatter, undermine, unbind. spoil, vacate, weaken, blot. rub, wipe. smash. cross. finish, slip. sink, strike. open
unwrap, uncork, Unclose.
unfold
uncoil.

Usage examples for undo

  1. What is it you cannot undo little Daisy? – Daisy in the Field by Elizabeth Wetherell
  2. It is one of the things we can't undo and must take as they come. – Half a Dozen Girls by Anna Chapin Ray
  3. You can't help what happened years ago- you can't undo it. – The Marriage of William Ashe by Mrs. Humphry Ward