Render coarse gallows humour for starters in French city (7)
I believe the answer is:
roughen
'render coarse' is the definition.
(to roughen is to make rough or coarse)
'gallows humour for starters in french city' is the wordplay.
'for starters' suggests taking the first letters.
'in' means one lot of letters goes inside another.
'french city' becomes 'rouen' (I've seen this in another clue).
The initial letters of 'gallows humour' is 'gh'.
'gh' put into 'rouen' is 'ROUGHEN'.
(Other definitions for roughen that I've seen before include "Make less smooth" , "chap" , "Gore Hun (anag)" , "rasp" , "Abrade" .)