Disgust, horrify (5)
I believe the answer is:
appal
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">disgust</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(appalling is a kind of disgusting)</span><br/ ><br/ >'<span class="explanation-format__original">horrify</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(Other definitions for appal that I've seen before include "Shock, horrify" , "exhibiting dismay" , "Put at rest (suspicion)" , "To shock, dismay" , "Outrage" .)