The story
Shortened form of aerothermodynamic duct.
Etymology from Wiktionary, CC BY-SA 4.0.
Today it means: A simple jet engine consisting essentially of a tube with a means of delivering fuel and ignition into the tube. The engine can only be started in a fast airflow. This type of engine is expected to be able to provide cruising speeds at Mach numbers of around 5 to 7 (5 to 7 times the speed of sound). Full definition →
Shortened form of aerothermodynamic duct.
Etymology from Wiktionary, CC BY-SA 4.0.