Diligent cadet died after training (9)
I believe the answer is:
dedicated
'diligent' is the definition.
(I've seen this before)
'cadet died after training' is the wordplay.
'after training' is an anagram indicator (train can mean to shape or control).
'cadet'+'died'='cadetdied'
'cadetdied' is an anagram of 'DEDICATED'.
(Other definitions for dedicated that I've seen before include "exclusive" , "Determined" , "Consecrated - single-minded" , "Committed" , "Devoted to a particular cause or purpose" .)