Helpful response to "Do you mind?" (3,2,3)
I believe the answer is:
not at all
'helpful response to do you mind?' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for not at all that I've seen before include "In no way" , "acceptance of apology" , "You're welcome" , "forget it" , "By no means - polite disclaimer" .)