This idiom means to calm down, slow down, or restrain one’s excitement or impatience, as if cooling the jets of an overheated engine. It conveys a call for composure, often used in personal, social, or informal contexts to temper eagerness or agitation. The phrase carries a tone of admonition, humor, or friendliness, reflecting cultural values of patience and the human tendency to rush. Its aviation imagery evokes a high-energy pause, resonating in scenarios like heated moments or anticipation. The idiom promotes restraint, making it a playful metaphor for calming down.

The phrase originated in mid-20th-century America, tied to jet aircraft and military slang for cooling engines, as noted in air force records. Its earliest recorded use appears in *The New York Times* (1950s), describing impulsive youth. The idiom gained traction in the 1960s, amplified by pop culture and TV, notably in *The Jetsons*. Its adoption, primarily in the U.S., stems from its modern imagery and applicability to impatience, with some use in Canada and Australia.