seventh heaven vs bliss

seventh heaven and bliss both are nouns.

Word	Noun	Adjective	Verb	Adverb
seventh heaven	Yes	No	No	No
bliss	Yes	No	No	No

As nouns, seventh heaven and bliss are synonyms defined as:

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

seventh heaven (noun)	bliss (noun)
a state of extreme happiness	a state of extreme happiness