Why is the bishop in chess called Слон?

I recently looked at Russian chess terminology, since I want to participate in the Moscow chess festival, but I am confused about the naming of the bishop. I know Слон means elephant, but in chess why the bishop called Слон not the knight? I think it would make more sense to call the knight, Слон, because in old Indian or Persian chess sets, the knights are elephants. Just questions and would like a clarification from you guys.