Chaps initially sound exasperated after this writer is gross (7)
I believe the answer is:
immense
'gross' is the definition.
(gross can mean massive or immense)
'chaps initially sound exasperated after this writer is' is the wordplay.
'chaps' becomes 'men' (chap can mean a man).
'initially' suggests taking the first letters.
'after' is a charade indicator (letters next to each other).
'this writer is' becomes 'I'm' (I am - referring to the crossword setter).
The initial letters of 'sound exasperated' is 'se'.
'men'+'se'='mense'
'mense' put after 'im' is 'IMMENSE'.
(Other definitions for immense that I've seen before include "Vast or enormous" , "Unusually great in size" , "Jumbo" , "Mammoth" , "Unctuously ingratiating" .)