vault of heaven vs empyrean

vault of heaven and empyrean both are nouns.

Word	Noun	Adjective	Verb	Adverb
vault of heaven	Yes	No	No	No
empyrean	Yes	Yes	No	No

As nouns, vault of heaven and empyrean are synonyms defined as:

vault of heaven and empyrean: the apparent surface of the imaginary sphere on which celestial bodies appear to be projected

Other synonyms of vault of heaven include celestial sphere, firmament, heavens, sphere, welkin.

vault of heaven (noun)	empyrean (noun)
the apparent surface of the imaginary sphere on which celestial bodies appear to be projected	the apparent surface of the imaginary sphere on which celestial bodies appear to be projected

vault of heaven (adjective)	empyrean (adjective)
	of or relating to the sky or heavens
	inspiring awe