Argument during light meal (6)
I believe the answer is:
tiffin
'light meal' is the definition.
(I've seen this before)
'argument during' is the wordplay.
'argument' becomes 'tiff' (I've seen this before**).
'during' becomes 'in' (I've seen this in other clues).
'tiff'+'in'='TIFFIN'
(Other definitions for tiffin that I've seen before include "Snack, light meal (dated)" , "Light Indian repast" , "(Anglo Indian) lunch" , "Indian midday meal" , "Light (Indian) meal" .)