Disturb; fluster (4)
I believe the answer is:
faze
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">disturb</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">fluster</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ ></span>
(Other definitions for faze that I've seen before include "Be disturbing" , "Disconcert, worry" , "Throw from" , "Disturb, disconcert" , "disconcerting" .)