Winter frost (4)
I believe the answer is:
hoar
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">winter frost</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for hoar that I've seen before include "A kind of white frost" , "Rime" , "Type of frost" , "Here are ice crystals" , "Greyish-white with age or frost" .)