Hairdo — skullcap (4)
I believe the answer is:
coif
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">hairdo</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that hairdo can be written as coif)</span><br/ ><br/ >'<span class="explanation-format__original">skullcap</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(coif is a kind of skullcap)</span><br/ ><br/ ></span>
(Other definitions for coif that I've seen before include "what can be made of lawn?" , "Cap worn by fundamentalist Mormon women: hairstyle" , "Headgear" , "Nun's cap" , "Dress the hair" .)