Mushroom with a brown cap (3)
I believe the answer is:
cep
'mushroom with a brown cap' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for cep that I've seen before include "Variety of mushroom" , "Edible mushroom" , "Porcino" , "Mushroom with a brown cap" , "Porcini mushroom" .)