Prefix with profit (3)
I believe the answer is:
non
'prefix with profit' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for non that I've seen before include "Prefix meaning not or none" , "Combining form meaning not" , "- - -stick" , "Prefixed negation of a word" , "Negative French word" .)