Perturb, discompose (8)
I believe the answer is:
unsettle
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">perturb</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >'<span class="explanation-format__original">discompose</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(unsettling is a kind of discomposing)</span><br/ ><br/ ></span>
(Other definitions for unsettle that I've seen before include "Make uneasy, disturb the calm of" , "Nettle us so as to disturb" , "'Disturb, unnerve (8)'" , "Trouble" , "Faze" .)