Sweetened tin passed away (7)
I believe the answer is:
candied
'sweetened' is the definition.
(candying is a kind of sweetening)
'tin passed away' is the wordplay.
'tin' becomes 'can' (synonyms).
'passed away' becomes 'died' ('die' can be a synonym of 'pass away').
'can'+'died'='CANDIED'
(Other definitions for candied that I've seen before include "Covered with sugar" , "no longer flattering" , "Crystallised" , "Sugary" , "Sugared" .)