Re: props
Didn't we go over this a couple of months ago? Engines use some sort of combustion, usually internal, for energy. Thus a steam engine, a diesel engine, a gasoline engine.
However an ELECTRIC MOTOR produces horsepower as does a compressed air MOTOR. Old Cub Cadet lawn mowers used both: A gasoline engine drove a hydraulic pump which powered a hydraulic motor at the rear axle.
The english language is quite dynamic. In common usage, most people use the two terms interchangeably and unless you are taking an engineering course, you will not be corrected. Typically, common usage becomes the accepted usage. In my day a BMW was called a "BIMMER". My kids call it a "BEEMER" and nothing is going to change them; indeed, sooner or later I will probably start to use their terminology.