Mushroom top (3)
I believe the answer is:
cap
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">mushroom top</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 cap that I've seen before include "'If the . . . fits, wear it' (3" , "Surpass with headwear" , "Limit (prices)" , "Soft headgear" , "One on head; excel" .)