I have always been led to believe that a engine burned fuel and a motor used electricity.
BINGO.........haha. Pretty much right on I think. Also ,all my FSM's refer to every different size as 3.5L engine or 4.7L engine etc......and they made the "darn dino juice burning thingys" so I just go by that. The starter motor is referred to in the FSM as a motor probably cause it gets battery juice and does not have any "infernal" combustion.