Polar covering (6)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">polar covering</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for icecap that I've seen before include "frozen summit" , "White mountain top" , "Frozen covering of polar regions" , "Frozen topping" , "Permanent covering in frozen Arctic regions" .)