Who here can explain the difference between a steam locomotive; "Appurtenance" and an "Appliance"?

Both terms are used in reference to the steam locomotive and its attached components such as air compressor, injector, lubricator, turbo-generator, etc...

The two terms must be close in definition, but with a critical small distinction.

Also, how which term would you use to categorize "Classification lamps" such as the old "Radial" Classification lamps as used on the early D&RG standard gauge and narrow gauge, and the ubiquitous Pyle National "globe" shaped classification lamps used on nearly ever major road from about the 1930's onward? Would those be; Appurtenances, Appliances or something else entirely?

Definitions I found;

Appurtenance; Something that, although detached, stands as part of another thing. An attachment or appendage to something else.

Appliance; A piece of equipment for adapting a tool or machine to a special purpose. An instrument or device designed for a particular use or function

Anyone want to try to sum this up?? This is what I am thinking;

Appliances must be; Air compressors, Brake parts, air signal systems and other parts that are on the locomotive but are parts of other systems (used for other than the locomotives primary purpose; locomotion).

Appurtenances must be; related to locomotion or the operation of the locomotive (injectors, fire box doors, stockers, steam valves, burner controls, etc). must be appurtenances.

What do you think?