seventh heaven vs cloud nine

seventh heaven and cloud nine both are nouns.

Word	Noun	Adjective	Verb	Adverb
seventh heaven	Yes	No	No	No
cloud nine	Yes	No	No	No

As nouns, seventh heaven and cloud nine are synonyms defined as:

Other synonyms of seventh heaven include bliss, blissfulness, walking on air.

seventh heaven (noun)	cloud nine (noun)
a state of extreme happiness	a state of extreme happiness