Motorcycle is just short for Motorized Bicycle. Bicycle is just a name for a 2 wheeled conveyance, be it peddled or propelled with a motor or engine. Modern use of the words just evolved them into very specific things, and today most people mean a pedaled bicycle when they say bicycle.
The propulsion methods are really the one variable. A Moped - Motor and Pedal - instead of calling it a Motor Pedal Cycle. Which is what most of us build on this site, and what most ebikes are considered.
That is actually the legal separation that many states and cities are using to define the legality of, and registration of, many ebikes. If it lacks pedals, it is an electric motorcycle.