Silk turned oily by cheese (7)
I believe the answer is:
taffeta
'silk' is the definition.
(I've seen this before)
'turned oily by cheese' is the wordplay.
'turned' says the letters should be written backwards.
'oily' becomes 'fat' (similar in meaning).
'by' says to put letters next to each other.
'cheese' becomes 'feta' (type of cheese).
'fat' backwards is 'taf'.
'taf'+'feta'='TAFFETA'
(Other definitions for taffeta that I've seen before include "A shiny silklike fabric" , "Thin silky material" , "fine material for dressing" , "fine stuff indeed!" , "Stiff, silky fabric" .)