Covered in lubricant (4)
I believe the answer is:
oily
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">covered in lubricant</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for oily that I've seen before include "Covered in lubricant" , "covered in grease" , "Unctuous" , "Oleaginous" , "Unpleasantly ingratiating" .)