While Railfanning and Model Railroading is a Hobby, Railroad History is available (and the (accurate) preservation of it is one of the goals of the BRHS (not that this is that list).
Bill and others are correct to point out that terminology did vary between railroads and even different parts of the same line.
That does not, however, give carte blanche to invent terms or propagate known incorrect ones. Over on the Passenger Car List an individual insists on calling diaphragms “pongers” and a number of people have picked up on that inexplicable made-up moniker. Likewise some Model Railroaders like to call a 2-8-0 a “Connie”…… a term I have yet to run into in any prototype railroad literature and only see as a reference to a series of three tailed prop airliners made by Lockheed (and a Greek restaurant in Berwyn at Harlem Avenue and the CB&Q that was a favorite after-IITMR club late night hangout).
The apparent or possible confusion brought about by calling a Fairmont or some such MOW machine a “motor car” when the same term was applied to a Gas-Electric is something that needs to be further researched. On the CB&Q early on distillate, gas, and diesel locomotives were referred to as “motors” so there probably is no confusion there.
Charlie Vlk