Oily fruit (5)
I believe the answer is:
olive
'oily fruit' is the definition.
(as in olive oil)
This is all the clue.
(Other definitions for olive that I've seen before include "Oil producer" , "Small green tree-fruit, nice in martini" , "Yellowy-green colour and fruit" , "It's branch is a symbol of peace" , "Green shade; its branch for peace" .)