Thanks, FL.
It seems like a common definition of engine is to "convert one form of energy into motion"... so by that broad def, it seems to me that "electric engine" seems a reasonable term, but I understand that obeying rules of popular parlance is worthwhile. Nonetheless, the categories and concepts fascinate me more, if only to highlight similarities and differences in the world of engines (and motors).
I began wondering how to classify a hot air ballon? I mean... it converts chemical energy into a force that's applied to body which ends with motion... like hot exhaust gasses in the cylinder of an engine pushing on a piston, there's hot air pushing on the skin of the balloon... although maybe the distinction between motion and lift/buoyancy are really significantly here. Still, the ways of creating the force are kinda related.
And then there's kites and sails... however, they don't convert energy - they merely use existing forces. Maybe a balloon could fall into that category too, in the sense that it doesn't convert energy, but rather takes advantage of force that's created from manipulating the environment.
That makes me wonder about horse drawn carriages too... or perhaps dog sleds... again forces are used to create motion, but there is no conversion of energy - merely a transference, so one could not call them "engines" I suppose.
Just hypothetical musing. Outstanding wastes of time