I vote for the dictionary definition. Mo(tor) Ped(al).
All the engine size limitations are legislative crap. Changing from 50cc to 70cc should have no effect on the definition of the vehicle itself. It may no longer fall into the State's definition of a road legal moped but it's still a moped. Place a V8 in a go-cart, add lights, electric start, whatever, it still doesn't make it a car.