The story
From jet + dryer. From being a device that projects a jet of air used to dry a surface.
Etymology from Wiktionary, CC BY-SA 4.0.
jet dryer
Today it means: A piece of racetrack maintenance equipment, a truck or trailer equipped with a gas turbine jet engine (which does not provide motive or electrical power), that provides copious amounts of hot air, which is used to blow dry the track surface. Full definition →