Wounded sergeant’s heroism (9)
I believe the answer is:
greatness
'heroism' is the definition.
(thesaurus)
'wounded sergeant's' is the wordplay.
'wounded' indicates an anagram (I've seen this in other clues).
'sergeants' with letters rearranged gives 'GREATNESS'.
(Other definitions for greatness that I've seen before include "Natal attribute or achievement or something thrust upon one!" , "Outstanding importance or largeness" , "Pre-eminence; high station" , "celebrity" , "Malvolio wasn't to fear being thrust into?" .)