- undo⇄noun undoer.
- undo⇄undo, transitive verb, -did,-done,-doing.
1. to unfasten and open; unloose and remove the wrapping of.
Ex. ""Please undo the package,"" she said.
2. to untie.
Ex. to undo a knot. I undid the string.
3. to do away with; caus