fairy ring vs fairy circle

fairy ring and fairy circle both are nouns.

Word	Noun	Adjective	Verb	Adverb
fairy ring	Yes	No	No	No
fairy circle	Yes	No	No	No

As nouns, fairy ring and fairy circle are synonyms defined as:

fairy ring and fairy circle: a ring of fungi marking the periphery of the perennial underground growth of the mycelium

fairy ring (noun)	fairy circle (noun)
a ring of fungi marking the periphery of the perennial underground growth of the mycelium	a ring of fungi marking the periphery of the perennial underground growth of the mycelium