Domestic fuel (3)
I believe the answer is:
gas
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">domestic fuel</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 gas that I've seen before include "Americans' petrol" , "Something delightful" , "Carbon dioxide, say" , "16 (US)" , "Form of fossil fuel" .)