The Collaborative International Dictionary of English v.0.48:
cloud nine \cloud" nine"\, cloud-nine \cloud"-nine"\n. a state of extreme or perfect happiness; used especially in the phrase on cloud nine. Syn: bliss, blissfulness, seventh-heaven. [WordNet 1.5 +PJC]WordNet (r) 3.0 (2006):
cloud nine n 1: a state of extreme happiness [syn: bliss, blissfulness, cloud nine, seventh heaven, walking on air]