cloud nine vs walking on air

cloud nine and walking on air both are nouns.

Word	Noun	Adjective	Verb	Adverb
cloud nine	Yes	No	No	No
walking on air	Yes	No	No	No

As nouns, cloud nine and walking on air are synonyms defined as:

Other synonyms of cloud nine include bliss, blissfulness, seventh heaven.

cloud nine (noun)	walking on air (noun)
a state of extreme happiness	a state of extreme happiness