Thin branch; realise (4)
I believe the answer is:
twig
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">thin branch</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">realise</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for twig that I've seen before include "Small part of a branch - suddenly understand" , "small piece in plane, say" , "A little stick" , "Suddenly see; branchlet" , "Get the idea" .)