fairy ring vs doughnut

fairy ring and doughnut both are nouns.

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

As nouns, doughnut is a hypernym of fairy ring; that is, doughnut is a word with a broader meaning than fairy ring:

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

Other hypernyms of fairy ring include anchor ring, annulus, halo, ring.

fairy ring (noun)	doughnut (noun)
a ring of fungi marking the periphery of the perennial underground growth of the mycelium	a small ring-shaped friedcake
	a toroidal shape