Definition of Engine

Noun: engine en-jun [N. Amer], en-jin [Brit]

Motor that converts thermal energy to mechanical work
Something used to achieve a purpose
"an engine of change"
A wheeled vehicle consisting of a self-propelled engine that is used to draw trains along railway tracks
- locomotive, locomotive engine, railway locomotive [Brit, Cdn], loco, railroad locomotive [N. Amer]
An instrument or machine that is used in warfare, such as a battering ram, catapult, artillery piece, etc.
"medieval engines of war"