annulus vs fairy ring

annulus and fairy ring both are nouns.

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

As nouns, fairy ring is a hyponym of annulus; that is, fairy ring is a word with a more specific, narrower meaning than annulus:

annulus: a toroidal shape
fairy ring: a ring of fungi marking the periphery of the perennial underground growth of the mycelium

Other hyponyms of annulus include fairy circle.

annulus (noun)	fairy ring (noun)
(Fungi) a remnant of the partial veil that in mature mushrooms surrounds the stem like a collar	a ring of fungi marking the periphery of the perennial underground growth of the mycelium
a toroidal shape