This is rather like trying to define what "art" is. Everyone is going to have a different idea that's hard to put into words.
The thing is, you usually know it when you see it, and most of the time everyone can agree.
I'm with
@Larry Jones , if you're trying to make your own game, then it will most likely stand on its own without worrying about this. If you're trying to copy another game, then that will show, too, and you SHOULD worry if that's the case. (And ask yourself why you're spending your time remaking a game that's already been done!)
If you're really concerned about a specific instance, it's best to get as many
brutally honest outside opinions as you reasonably can. First let them see the game on its own and ask what they think of it. If they don't mention the game you think it's similar to, ask them about it after you get their first impression. If the majority of people know both games and still think they're different, you're probably good.