Pronunciation: (un-dOO'),[key] —v.t.,-did, -done, -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.