Art medium (4)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">art medium</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for oils that I've seen before include "7's paint medium" , "paintings?" , "Well-produced" , "Liquids for frying" , "Viscous substances kept in silo" .)