Undo \un*do"\, v. t. [AS. und?n. See 1st Un-, and Do to perform.]

1. To reverse, as what has been done; to annul; to bring to naught

   What's done can not be undone. --Shak

   To-morrow, ere the setting sun, She 'd all undo that she had done. --Swift

2. To loose; to open; to take to piece; to unfasten; to untie; hence, to unravel; to solve; as, to undo a knot; to undo a puzzling question; to undo a riddle. --Tennyson

   Pray you, undo this button. --Shak

   She took the spindle, and undoing the thread gradually, measured it. --Sir W Scott

3. To bring to poverty; to impoverish; to ruin, as in reputation, morals, hopes, or the like; as, many are undone by unavoidable losses, but more undo themselves by vices and dissipation, or by indolence

   That quaffing and drinking will undo you, --Shak

4. Cancel or reverse an action or its effect; "I wish I could undo my actions"
5. Deprive of certain characteristics [syn: unmake] [ant: do]
6. Make undone; revert to the original condition or situation; "You cannot undo the damage!"