Cloud 9 is an
idiom for a state of joy,
euphoria, or extreme happiness. Usually "cloud 9" is coupled with the "on"
preposition.
"Those
chocolate bunny ears were so good I was on cloud 9! I love consuming simulated fluffy animals!"
There are a couple theories regarding this expression's origin. An early cloud classification system had nine levels of
cloud classification. The
cumulonimbus clouds, the most fluffy
cotton candyish of clouds, were slotted in at the 9 position. Clouds, heaven,
angels have long been associated. A true state of euphoria might be considered being up on the cloud 9 level, upon the most aesthetically pleasing of clouds.
Alternatively, the number 9 is considered a very pure number. It's a
trinity of trinities. Three times three. Hence the expression "
dressed to the nines", which means well dressed. So being up on a cloud numbered 9 is surely a good thing, if you adhere to a childhood fantasy of heaven. For those who believe
oxygen deprivation has the greater downside, well, it's a somewhat silly
allusion.
A strong possibility for the origin comes to us from
Buddhism. In Buddhism one ascends 10 clouds. Cloud 9 is a state of
enlightenment, where one's acts are done without regard for the self. However, the expression's popular use makes this suspect. Being on cloud 9 almost always refers to a rather selfish state of self satisfaction.