After start of argument fight roughly (5)
I believe the answer is:
about
'roughly' is the definition.
('about' can be a synonym of 'roughly')
'after start of argument fight' is the wordplay.
'after' means one lot of letters go next to another.
'start of' says to take the initial letters.
'fight' becomes 'bout' ('bout' can be a synonym of 'fight').
The initial letter of 'argument' is 'a'.
'a' put next to 'bout' is 'ABOUT'.
(Other definitions for about that I've seen before include "Approximately, or in vicinity" , "not far away" , "In the area of or in relation to" , "Close to" , "Nearly" .)