noun
1. : a ring of mushrooms ( Marasmius oreades or other basidiomycetes) that is produced at the periphery of mycelium which has grown centrifugally from an initial growth point and that increases in diameter from year to year ; also : a ring of luxuriant vegetation associated with these mushrooms that also increases in diameter from year to year
2. or fairy-ring mushroom : a mushroom (especially Marasmius oreades ) that commonly grows in fairy rings