Oily compound (5)
I believe the answer is:
lipid
'oily compound' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for lipid that I've seen before include "Organic compound" , "Oil, say" , "oily substance" , "One of the essential structural components of living cells" , "Insoluble fatty acid" .)