The term “cloud nine” is typically used to refer to a state of happiness and euphoria, though it can instead be used to refer to intoxication or feelings of light-headedness. This term’s exact origins are fairly difficult to discern, though one particularly popular, and almost universally dismissed, explanation relates to a numerical system said to have been used at one time by the Weather Bureau in the US for designating the height of clouds. Regardless of its origins, most people use the phrase “being on cloud nine” to indicate extreme happiness or satisfaction with life.
“Cloud nine” is a term typically associated either with general happiness, regardless of the cause of that happiness, or a state of inattentiveness or daydreaming. This term is likely American in origin and initial usage, though it could have come from a number of different sources. It has been used within numerous drug cultures, often associated with illegal narcotics that are often consumed through burning and inhalation of the smoke produced by them, such as marijuana or “crack” cocaine. In this usage, “cloud nine” can have a negative connotation, as it typically refers to a state of euphoria that may be experienced by someone under the sway of the drug, and can indicate physical incapacitation due to this intoxication.
Many people use the expression “on cloud nine” to refer to a state of general happiness, or daydreaming. This may be associated with other terms like “having one’s head in the clouds” and the numerical value of the expression seems to change in different uses over time. There is evidence of people using the terms “cloud seven” and “cloud eight” as well as “cloud nine,” all with the same meanings. “Cloud seven” even seems to indicate a relationship with the notion of “seventh heaven” and positive feelings of happiness associated with such an elevated state.
Some sources cite the origin of “cloud nine” as an old system once used by the US Weather Bureau for categorizing clouds based on their height. There is little evidence to support this claim, however, and not much evidence to show that such a system was ever used. What evidence there is, however, suggests that 10 would have been the highest level of cloud, making the use of “nine” and the variable nature of the numerical value in older uses further discredit this source. It is likely that “cloud nine” simply stems from an association with clouds as a place of happiness away from the cares of a terrestrial world, and that the numerical value has been largely arbitrary.