motor that converts thermal energy to mechanical work
"The steam engine converted the heat from burning coal into the mechanical power needed to drive the train wheels."
a wheeled vehicle consisting of a self-propelled engine that is used to draw trains along railway tracks
"The heavy diesel engine pulled the passenger cars smoothly through the mountain pass."
an instrument or machine that is used in warfare, such as a battering ram, catapult, artillery piece, etc.
"medieval engines of war"
A large construction used in warfare, such as a battering ram, catapult etc.
"The medieval siege engine was so massive that it required fifty men just to move its wheels forward toward the castle walls."
In plain English: An engine is a machine that creates power to move vehicles or run equipment.
"The car engine was making a loud noise before breaking down."
Usage: In modern everyday usage, an engine is a machine that converts energy into mechanical motion to drive vehicles or equipment. Do not use this term to describe ancient siege weapons like battering rams or catapults, which are historically referred to as engines of war only in specific literary contexts.
To equip with an engine; said especially of steam vessels.
"The shipyard spent months to engine the new cargo vessel before its maiden voyage on the river."
In plain English: To engine means to move something forward by using an engine's power.
"The new software engine will quickly process your request."
Usage: The verb form of "engine" means to power or drive something with an engine, such as when a ship is fitted with a steam motor. In modern usage, people rarely use this specific meaning and instead say that a vessel is "engined" or simply "powered."
The word "engine" comes from the Old French engin, which originally meant "skill" or "cleverness." Over time, it shifted in meaning to refer specifically to a war machine before entering Middle English.