1
general::
Phrase(s): on cloud nine
Fig. very happy. • When I got my promotion, I was on cloud nine. • When the check came, I was on cloud nine for days.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Blissfully happy, as in Ever since he proposed to her, her parents have been on cloud nine. The exact allusion of nine in this term is unclear, and different figures, especially seven (perhaps alluding to SEVENTH HEAVEN), are sometimes substituted. [Colloquial; mid-1900s]
American Heritage Idioms