The ship experiences accele forward, and the occupants inside experience that as a gravity like effect.
Right - Newton's 3rd law. As I mentioned in my side note, I don't know if a singular word exists for that. "Action-reaction" is a term I've seen, but that's pretty clunky. Afaik, a new word would have to be coined to express that interaction. If I had to suggest something, my off-the-cuff, "probably wrong in even more ways" idea would be "pronertia".