In rough terms a boxing match (5)
I believe the answer is:
about
'in rough terms' is the definition.
'a boxing match' is the wordplay.
'boxing match' becomes 'bout' (I've seen this before).
'a'+'bout'='ABOUT'
(Other definitions for about that I've seen before include "Circa" , "round" , "Moving" , "On the subject of, approximately" , "nearby" .)