Whole-hearted cadet died in battle (9)
I believe the answer is:
dedicated
'whole-hearted' is the definition.
Both the answer and definition are adjectives.
Maybe you can see an association between them that I can't see?
'cadet died in battle' is the wordplay.
'in battle' indicates an anagram (I've seen this in other clues).
'cadet'+'died'='cadetdied'
'cadetdied' anagrammed gives 'DEDICATED'.
Can you help me to learn more?
(Other definitions for dedicated that I've seen before include "Devoted to a task or purpose" , "Committed" , "Hard working" , "Customised" , "exclusive" .)