engineer; engineering officer
Refers to a licensed engineer responsible for operating and maintaining engines, boilers, or machinery on trains, ships, or aircraft. In modern contexts, often replaced by more specific titles like 機関長 (chief engineer) or 運転士 (train operator), but still used in historical or formal settings.
彼は船の機関士として世界中を航海した。
He sailed around the world as a ship's engineer.
The steam locomotive engineer operated the train while shoveling coal.
機関士 specifically means an engineer who operates and maintains a train's engine or a ship's machinery, whereas 運転士 focuses on actually driving or steering the vehicle.
Compound of 機関 (engine, machinery) and 士 (person with a certain qualification or occupation).