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
While watching a broadcast about the Artemis moon launch, Josh from Jacksonville, Florida, noted that amid all the precise language, scientists describing precise orbital adjustments used the word tad, as in just a tad, which seemed like the...
What’s a gongoozler? Today a gongoozler is anyone who just stands around watching things, but the term originated in the slang of British canal workers, who specifically applied it to onlookers inordinately interested in their work. A 1904 glossary...
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.