Inedible fungus (9)
I believe the answer is:
toadstool
'inedible fungus' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for toadstool that I've seen before include "Capped fungus" , "Umbrella-shaped fungus" , "a potentially toxic development" , "Poisonous fungus" , "Common fungus" .)