Aeropause

Part of speech: noun

Definitions

1. The boundary in the atmosphere where gas density diminishes sharply, indicating the transition to the vacuum of space is reached
2. The distinct altitude within the Earth's atmospheric layers where air pressure dwindles, signaling the onset of space
3. The transition zone in the atmosphere where the density of gases drops significantly, marking the boundary between the atmosphere and outer space

Etymology: "Aeropause" is a modern coinage built from two pieces: "aero-", from Greek "aēr" meaning air, and "pause", a word that here plays on the notion of a boundary or stopping point. The sense is a stopping place for the atmosphere itself, the altitude where the air becomes too thin to support ordinary flight and the environment starts to shade into space. The pairing is deliberate wordplay in the style of "-pause" terms such as "tropopause" and "stratopause", which name the boundaries between layers of the atmosphere. Coined by analogy with those terms, it borrows their structure to name a boundary that is less a sharp line than a zone where pressure falls away steadily.