Returned rotten old fruit (5)
I believe the answer is:
olive
'fruit' is the definition.
(I've seen this before)
'returned rotten old' is the wordplay.
'returned' shows that the letters should be reversed in order.
'rotten' becomes 'evil' (I can't explain this - if you can you should give a lot more credence to this answer).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'evil'+'o'='evilo'
'evilo' written backwards gives 'OLIVE'.
Can you help me to learn more?
(Other definitions for olive that I've seen before include "Mediterranean fruit or greenish colour" , "yellowish green" , "Girl's name; tree" , "Girl's name - colour" , "Fruit giving oil" .)