Rendered tune backwards, possibly from drink (7)
I believe the answer is:
sangria
'drink' is the definition.
(type of alcoholic drink)
'rendered tune backwards' is the wordplay.
'rendered' becomes 'sang' (singing is a kind of rendering).
'tune' becomes 'air' (air can mean a piece of music).
'backwards' is a reversal indicator.
'air' written backwards gives 'ria'.
'sang'+'ria'='SANGRIA'
'possibly from' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for sangria that I've seen before include "Spicy Spanish wine drink" , "Spanish spiced wine" , "Spanish drink of red wine, sugar and fruit" , "Drink - Iran gas (anag)" , "Red wine, fruit juice, sugar and spices" .)