Covered in lubricant (4)
I believe the answer is:
oily
'covered in lubricant' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for oily that I've seen before include "Covered in lubricant" , "covered in grease" , "Unctuous" , "Oleaginous" , "Unpleasantly ingratiating" .)