We hear forty of the Romans do better (5)
I believe the answer is:
excel
'do better' is the definition.
(I've seen this in another clue)
'we hear forty' is the wordplay.
'we hear' indicates a 'sounds like' (homophone) clue.
'forty' becomes 'xl' (Roman numerals).
'xl' is a homophone of 'EXCEL'.
'of the romans' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for excel that I've seen before include "Do particularly well" , "Predominate in" , "Be superior to" , "surpass all others" , "Be the best" .)