Thick treacle (8)
I believe the answer is:
molasses
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">thick treacle</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 molasses that I've seen before include "Syrupy stuff" , "Slow runner" , "Thick dark syrup made from sugar cane" , "US name for treacle" , "Black treacle" .)