Engine - Definition
engine
n 1: motor that converts thermal energy to mechanical work
2: something used to achieve a purpose; "an engine of change"
3: a wheeled vehicle consisting of a self-propelled engine that
is used to draw trains along railway tracks [syn:
locomotive, engine, locomotive engine, railway
locomotive]
4: an instrument or machine that is used in warfare, such as a
battering ram, catapult, artillery piece, etc.; "medieval
engines of war"