An edible fungus (8)
I believe the answer is:
mushroom
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">an edible fungus</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for mushroom that I've seen before include "grow quickly" , "increase hugely" , "that may be edible?" , "Food fungus" , "Balloon" .)