Fairy ring champignon

from The Collaborative International Dictionary of English v.0.48

Champignon \Cham*pi"gnon\, n. [F., a mushroom, ultimately fr. L.
   campus field. See {Camp}.] (Bot.)
   An edible species of mushroom ({Agaricus campestris}).
   [1913 Webster]

   {Fairy ring champignon}, the {Marasmius oreades}, which has a
      strong flavor but is edible.
      [1913 Webster]