[Capitalist Eric]

Actually, according to Websters definitions, either term could be used interchangeably.

Well, Websters doesn't get into the technical aspects of many things...

An engine converts chemical energy into mechanical energy, while a motor converts electrical (or magenetic) energy into mechanical energy...
And for the record, a generator converts mechanical energy into electrical or chemical energy (the latter is relatively rare, as a percentage of generator applications).

Be well.

[Dan Evans]

An engine converts chemical energy into mechanical energy, while a motor converts electrical (or magenetic) energy into mechanical energy...

Unless it's a solid fuel rocket -- which is called a rocket motor.