Not entirely prepared to accept my grievance (5)
I believe the answer is:
score
'grievance' is the definition.
('score' can be a synonym of 'grievance')
'not entirely prepared to accept my' is the wordplay.
'not entirely' means to remove the last letter.
'prepared' becomes 'set' (I've seen this before).
'to accept' indicates putting letters inside.
'my' becomes 'cor' (I've seen this in other clues).
'set' with its final letter taken away is 'se'.
'se' placed around 'cor' is 'SCORE'.
(Other definitions for score that I've seen before include "Result" , "Nick; twenty" , "Grade; twenty" , "Number of runs" , "Tally; scratch" .)