Take apart (4)
'take apart' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for undo that I've seen before include "Loosen or reverse" , "Cancel - destroy" , "Bring to nought" , "Loosen; annul" , "Remove the wrapping" .)
'take apart' is the definition.
(I know that take apart can be written as dismantle)
This is all the clue.
(Other definitions for dismantle that I've seen before include "Unrig" , "To demolish" , "Take to pieces" , "strike" , "Strip down" .)