Pal has an interesting origin.
Originally meaning “accomplice” rather than “friend”, it was borrowed from the Angloromani phal in the 18th century. This in turn comes from Romani phral, from the Sanksrit bhrātṛ meaning “brother”. bhrātṛ and brother derive from the same PIE root so it is interesting that its descendants made their way into English via such different routes.
(While learning this I also found out that Polly is a pet form of Molly, which in turn is a pet form of Mary, and that moll meaning prostitute has the same origin. Also, OED marks this sense of moll as rare which seems a bold claim. Gotta love wandering around the OED.)