Powerful fellow supports joke (7)
I believe the answer is:
pungent
'powerful' is the definition.
'fellow supports joke' is the wordplay.
'fellow' becomes 'gent' (I've seen this before**).
'supports' means one lot of letters go next to another (bottom letters provide a support for the top ones).
'joke' becomes 'pun' (punning is a kind of joking).
'gent' after 'pun' is 'PUNGENT'.
(Other definitions for pungent that I've seen before include "Smelly" , "Offensive" , "With a fifteen ac smell/taste" , "Biting" , "Acrid to smell" .)