equinoctial vs equinoctial circle

equinoctial and equinoctial circle both are nouns.

Word	Noun	Adjective	Verb	Adverb
equinoctial	Yes	Yes	No	No
equinoctial circle	Yes	No	No	No

As nouns, equinoctial and equinoctial circle are synonyms defined as:

equinoctial and equinoctial circle: the great circle on the celestial sphere midway between the celestial poles

Other synonyms of equinoctial include celestial equator, equinoctial line.

equinoctial (noun)	equinoctial circle (noun)
the great circle on the celestial sphere midway between the celestial poles	the great circle on the celestial sphere midway between the celestial poles

equinoctial (adjective)	equinoctial circle (adjective)
relating to an equinox (when the lengths of night and day are equal)
relating to the vicinity of the equator