As a noun, diesel is a type of fuel made from petroleum, used in some cars, trucks, and machines. It can also mean a diesel engine or vehicle that runs on this fuel; as an adjective, it describes things related to this type of engine.
Named after Rudolf Diesel, the German engineer who invented the diesel engine in the late 19th century. The engine and fuel took his surname as a proper noun that became a common noun.
Diesel began as a person’s name, then spread to engines, fuel, and even fashion brands. Diesel engines are more efficient than gasoline ones, which is why they dominate heavy transport—even as cleaner alternatives grow.
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