Refuses dialogue after last month (8)
I believe the answer is:
declines
'refuses' is the definition.
('decline' can be a synonym of 'refuse')
'dialogue after last month' is the wordplay.
'dialogue' becomes 'lines' (I've seen this in another clue).
'after' is a charade indicator (letters next to each other).
'last month' becomes 'dec' (short for December, last month of the year).
'lines' put after 'dec' is 'DECLINES'.
(Other definitions for declines that I've seen before include "Refuses to be silenced" , "Silenced in descents" , "Gradually decreases" .)