Terrifying, spine-chilling (13)

I believe the answer is:
bloodcurdling
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">terrifying</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >'<span class="explanation-format__original">spine-chilling</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for bloodcurdling that I've seen before include "Scary" , "Horrific" , "Causing horror" , "Horrible (of a scream?)" , "Terrifying (threats)" .)