Voiced private resentment (7)
I believe the answer is:
rancour
'resentment' is the definition.
(synonyms)
'voiced private' is the wordplay.
'voiced' shows a homophone (sound like).
'private' becomes 'ranker' (ranker can informally mean a military private).
'ranker' sounds like 'RANCOUR'.
(Other definitions for rancour that I've seen before include "Long-lasting bitterness" , "Feeling of bitterness or dislike" , "Deep-seated hostility" , "Bitter feeling or ill will" , "Antipathy" .)