cloud nine vs seventh heaven

cloud nine and seventh heaven both are nouns.

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

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

Other synonyms of cloud nine include bliss, blissfulness, walking on air.

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