Also, is there a general naming convention for religions? I know many of them end in -ism and so on, but what about the first part of the name? Christianity, obviously, is "followers of Christ", but I've no idea where names such as Judaism or Islam take the first part from. If I can't come up with a plausible name for a religion, I don't need to call it anything specific, but it would be easier to, especially if I plan to have two or more faiths in the story.
edited because I do honestly know Buddhism comes from Buddha.