Mesmerising (8)
I believe the answer is:
hypnotic
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">mesmerising</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 hypnotic that I've seen before include "Mesmerizing" , "Mesmerising" , "Entrancing" , "Mesmeric" , "Trance-inducing" .)