Thin strand
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">thin strand</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 wisp that I've seen before include "Slight trace" , "Small streak of smoke or cloud" , "Gauzy strand" , "whose will is so elusive?" , "Small thin bunch/strand (of something)" .)