A mushroom is not a mush, nor is it a room. It is a fungus.
A toadstool is not a toad, and it is not a stool. It is a fungus.
And as Matt Groening informed us in his wonderful book School Is Hell (he knew: he went to the same school that I did), a fish stick is not a fish, nor is it a stick. It is a fungus.
Evil Mad Scientist Quiz: Is it a fungus?