astronomy vs date of reference

astronomy and date of reference both are nouns.

Word	Noun	Adjective	Verb	Adverb
astronomy	Yes	No	No	No
date of reference	Yes	No	No	No

astronomy (noun)	date of reference (noun)
the branch of physics that studies celestial bodies and the universe as a whole	(astronomy) an arbitrarily fixed date that is the point in time relative to which information (as coordinates of a celestial body) is recorded