I thought the term was originally "motor engine" (a piece of engineering that produces motion) in the same way we can have a "compute engine" or a "siege engine

I thought the term was originally "motor engine" (a piece of engineering that produces motion) in the same way we can have a "compute engine" or a "siege engine" or a similar name for any other _ingenious_ creation. From there we tend to shorten it to either motor or engine. Perhaps in current times people here the terms "combustion engine" and "electric motor" most commonly and assume there is an implied distinction.