Remember, you are setting the internal name that Inform uses to refer to the action (“Starting”) but that is separate from the list of words that the parser uses to understand the action from the player. For example, there is only one name for the action of leaving an enterable thing (“exiting”) but the parser will understand EXIT, LEAVE, GET OUT, GET OFF…
Sequitur, I added that line, but the parser still tells me: “I didn’t understand that sentence.” when I tell it to start engine, which I defined as a thing. I tried both