Died last month, relieved of pain (8)
I believe the answer is:
deceased
'died' is the definition.
('decease' can be a synonym of 'die')
'last month relieved of pain' is the wordplay.
I cannot quite see how this works, but
'month' could be 'dec' (abbreviation for December) and 'dec' is located in the answer.
'relieved' could be 'eased' (easing is a kind of relieving) and 'eased' is present in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for deceased that I've seen before include "Late" , "No longer living" , "departed" , "Passed away" , "Recently dead" .)