Hat's edge (4)
I believe the answer is:
brim
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">hat's edge</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for brim that I've seen before include "The edge of a cup or glass" , "Circumference" , "Upper edge" , "Top edge of cup etc" , "Lip; part of a hat" .)