Poisonous fungus (9)
I believe the answer is:
toadstool
'poisonous fungus' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for toadstool that I've seen before include "Something poisonous" , "Umbrella-shaped fungus" , "Support for little people" , "jack-o'-lantern?" , "Common fungus" .)