I spent a couple of days this week at a philosophy conference. It was really interesting, especially as some of the talks were about the philosophy of language. On the first evening, I went to the pub with some of the philosophers and we talked about things I didn't understand all night. One of those things was metaphysics, which I had of course heard of, but didn't know what it was. We talked about it and its relation to physics, and I think I kind of now know vaguely what sort of a thing it is.
At some point I used the word 'metaphysicist' to describe someone who studies metaphysics, and was told that it is actually 'metaphysician'. This surprised me, because I formed the word without really thinking about it (which indicates that the word-formation process I used is highly productive), but probably on the basis of 'physicist' - someone who studies physics. 'Physician' is a word as well, of course, but it means basically the same as 'doctor'. The suffixes -ian and -ist are both used to form nouns meaning 'someone who does X'. Someone on Stack Exchange suggests -ian is more general and -ist more specialist, and this article by Laurie Bauer notes that -ician gained a 'trivialising' effect at some point around a century ago (though it's since lost that negative connotation).
I suspect it might be an effort on the part of metaphysicians to distance themselves from physicists. Or maybe there are people who, like me, enjoy being contrary and using the other one (I frequently refer to myself as a linguistician).