Fill with horror (5)
I believe the answer is:
appal
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">fill with horror</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for appal that I've seen before include "exhibiting dismay" , "To shock, dismay" , "Cause to be unpleasantly surprised" , "Greatly dismay" , "Scandalise" .)