seventh heaven vs blissfulness

seventh heaven and blissfulness both are nouns.

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

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

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

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