Strong chap depressed by witticism (7)
I believe the answer is:
pungent
'strong' is the definition.
(I've seen this before)
'chap depressed by witticism' is the wordplay.
'chap' becomes 'gent' (I've seen this in other clues).
'depressed by' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'witticism' becomes 'pun' (pun is a kind of witticism).
'gent' put after 'pun' is 'PUNGENT'.
(Other definitions for pungent that I've seen before include "Strong and sharp" , "spicy" , "Sharply tasting or smelling" , "Acrid; sarcastic (humour)" , "With a sharp taste or smell" .)