Talked of private grudge (7)
I believe the answer is:
rancour
'grudge' is the definition.
The definition and answer can be both feelings as well as being singular nouns.
Maybe there's an association between them I don't understand?
'talked of private' is the wordplay.
'talked of' indicates a 'sounds like' (homophone) clue.
'private' becomes 'ranker' (ranker can informally mean a military private).
'ranker' sounds like 'RANCOUR'.
Can you help me to learn more?
(Other definitions for rancour that I've seen before include "Malicious hostility" , "Spiteful ill-feeling" , "Bad feeling and resentment" , "Hard feelings" , "Bitterness and ill will" .)