What makes an Arabic word Arabic and a Persian word Persian?

So far, I haven't looked at that much Arabic and I can't learn every single word because I don't understand the characters and in my older dictionary, some of them had no sound. When I got my Lingo Traveler Dictionary, I looked at and learned my first few Persian words because I saw what they looked like now. In speaking of Persian, there is also called a cat with that name and it's also a Pokemon. So I went to look up the word for Persian in all languages especially for Arabic and Persian. What baffles me is that Persian is called Farsi as an endonym and that dictionary tells me in Arabic Persian is farisee and in Persian, Persian is irani with a little accent mark on top of the a shaped like this: ^. I could be wrong and I've been studying German and Japanese and attempting to improve my Spanish although I probably won't use it as much because I'll use English, German, and Japanese more often than Spanish and I know what makes a word English and what makes a word German and what makes a word Japanese and what makes a word Spanish. Grammar flow and word order!