walking on air vs cloud nine

walking on air and cloud nine both are nouns.

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

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

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

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