Fungal growth (5)
I believe the answer is:
mould
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">fungal growth</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 mould that I've seen before include "Crumbly soil" , "die?" , "Furry fungus" , "Cause of discoloration" , "Mildew" .)