bliss vs seventh heaven

bliss and seventh heaven both are nouns.

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

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

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

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