Slick substance (3)
I believe the answer is:
oil
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">slick substance</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for oil that I've seen before include "Type of fuel" , "Viscous substance as lubricant" , "what can be seen on iceberg" , "Anoint" , "Liquid fuel" .)