halo vs fairy ring

halo and fairy ring both are nouns.

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

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

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

Other hyponyms of halo include fairy circle.

halo (noun)	fairy ring (noun)
an indication of radiant light drawn around the head of a saint	a ring of fungi marking the periphery of the perennial underground growth of the mycelium
a circle of light around the sun or moon
a toroidal shape