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
We tend to take the index of a book for granted, but centuries ago, these helpful lists were viewed with suspicion. Some even worried that indexes would harm reading comprehension! A witty new book tells the story. Plus, the Latin term bona fides...
An acclaimed poet’s tender poem about holding a newborn for the first time reflects a complex swirl of emotions. And: A caller finds that in her workplace, the expression out of pocket can mean very different things: either “being unavailable” or...
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.