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
Advice about college essays from the winner of a top prize for children’s literature: Kelly Barnhill encourages teens to write about experiences that are uniquely their own, from a point of view that is theirs and no one else’s. Plus, why do we say...
A new book about how animals perceive their environment reveals immense worlds beyond our own. A bee can see ultraviolet light, catfish have taste buds all over their bodies, and manatees use highly sensitive lips to examine nearby objects. Also...
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.