Oleaginous (4)
I believe the answer is:
oily
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">oleaginous</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for oily that I've seen before include "Smooth, ingratiating" , "Viscous" , "Like a lot of fish" , "Unctuous" , "Covered in lubricant" .)