Late December abated (8)
I believe the answer is:
deceased
'late' is the definition.
(I've seen this in another clue)
'december abated' is the wordplay.
'december' becomes 'Dec' (synonyms).
'abated' becomes 'eased' (I've seen this in another clue).
'dec'+'eased'='DECEASED'
(Other definitions for deceased that I've seen before include "Totally bereft of life" , "departed" , "Defunct" , "Passed away" , "Pushing up the daisies" .)