any saprotrophic basidiomycetous fungus of the family Agaricaceae, having gills on the underside of the cap. The group includes the edible mushrooms and poisonous forms such as the fly agaric
2.
the dried spore-producing bodies of certain fungi, esp Polyphorus officinalis (or Boletus laricis), formerly used in medicine
[C16: via Latin agaricum, from Greek agarikon, perhaps named after Agaria, a town in Sarmatia]