unass v. to dismount or disembark (a vehicle); to get off of (something); to unseat (someone); to leave (somewhere). Editorial Note: This term dates back to at least the 1960s and the Vietnam War. It is especially associated with the military, from where it has spread to politics and aeronautics. (source: Double-Tongued Dictionary)
Further reading
In the 15th century, the word respair meant “to have hope again.” Although this word fell out of use, it’s among dozens collected in a new book of soothing vocabulary for troubled times. Plus, baseball slang: If a batter...
Asthenosphere, a geologist’s term for the molten layer beneath the earth’s crust, sparks a journey that stretches all the way from ancient Greece to the author of Uncle Tom’s Cabin. Plus: What the heck is a dogberg? It’s when...
This term was in use in the Army in the ‘50’s. I first heard it in 1955, when its meaning was “get up off of” as in: “Un-ass that chair!/rack!/bench!” etc.