An engine that makes power by burning a continuous stream of fuel and air: A jet engine moves a plane or car forward by firing a stream of hot gas backward; a scientific idea known as action and reaction, or Newton's third law.

A very tired and unpleasant feeling which a person sometimes gets when he or she travels by aircraft somewhere far away: Gerda had bad jet lag after her last trip overseas.

Descriptive of being very tired and lacking physical energy after a long flight: Walter's jet lagged sister had to recuperate and readjust to her normal life after her flight home from Canada back to Germany.