More gelid (5)
I believe the answer is:
icier
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">more gelid</span>' is the definition.<br/ ><span class="explanation-format__explanation">('icy' can be a synonym of 'gelid')</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for icier that I've seen before include "More slippery" , "increasingly frigid" , "More chilly" , "rather cold" , "with more reserve" .)