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Is "engine" appropriate to use here? It seems to just be the combustion chamber, similar to the article last week about the rocket test in India. It's cool research, but I don't know that the engine process matters much when you compare this to what SpaceX is doing with their engines and reducing the complexity of the moving parts, not just the static ones.

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While the terms can change over time, my understanding in ME circles is that "engine" is usually referring something that converts a source of energy into a force. So in this case, a device is using chemical energy (LOX + kerosene) into thrush (5kN) so it would meet the definition of an "engine."

Err... almost. An engine is something that has significant engineering effort put into it, you can see that the words are cognate. A motor is (usually an engine) that converts potential (stored) energy into motion, by way of some force. I do believe that motor and motion are also cognate.

But outside the etymologies, there is no standard, agreed upon definition for either the term engine nor motor. I personally like these etymology-based definitions (otherwise how do you excuse the term "siege engine") but it's not a hill I'd die on.

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