Steam engine and Steam locomotive

Steam engine noun - External-combustion engine in which heat is used to raise steam which either turns a turbine or forces a piston to move up and down in a cylinder.

Steam locomotive and steam engine are semantically related in locomotive engine topic. In some cases you can use "Steam locomotive" instead a noun phrase "Steam engine".

Steam locomotive noun - A locomotive powered by a steam engine.

Steam engine and steam locomotive are semantically related (American) in locomotive engine topic. You can use "Steam engine" instead a noun phrase "Steam locomotive".