Icebox (6)
I believe the answer is:
cooler
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">icebox</span>' is the definition.<br/ ><span class="explanation-format__explanation">(cooler is a kind of icebox)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for cooler that I've seen before include "Prison - less warm" , "less enthusiastic" , "Fan" , "It's not so hot" , "more sophisticated" .)