Ah! I understand, now. Thanks for clarifying.

I mostly understand "sentient" as most people use the term as the second meaning. Eliezer in particular seems to use "sentient" and "person" pretty much interchangeably here, for example, without really defining either, so I understand him to use the word similarly.

The latter, applied to the real world, sounds rather more like "soul" than anything coherent and obvious.

Were I inclined to turn this assertion into a question, it would probably be something like "what properties does a typical adult have that a typical 1-year-old lacks which makes it more OK to kill the latter than the former?"

Is that the question you're asking?