It is not possible (2,3,2)
I believe the answer is:
no can do
'it is not possible' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for no can do that I've seen before include "Bring-a-bottle party?" , "That's out of the question!" , "Unable to help" , "Absolutely not!" , "That's not possible" .)