Wicked ring brought back oil producer (5)
I believe the answer is:
olive
'oil producer' is the definition.
(I've seen this in another clue)
'wicked ring brought back' is the wordplay.
'wicked' becomes 'evil' (synonyms).
'ring' becomes 'o' (letter resembling a ring).
'brought back' shows that the letters should be reversed in order.
'evil'+'o'='evilo'
'evilo' in reverse letter order is 'OLIVE'.
(Other definitions for olive that I've seen before include "Type of green" , "One's stoned" , "Oil-yielding tree" , "Small green tree-fruit, nice in martini" , "woman" .)