In particular, I'm thinking of the words 名人, 玄人, 博士, 専門家, 達人, 巨匠, 通, and 有識者.
I have a vague idea that 玄人 is most often used for an expertise which is "casual" (eg: このゲームの玄人), and that 博士 generally seems to have qualifications, though not necessarily a PhD, but beyond that, I don't really have a good grasp on how these differ.
(I didn't include エキスパート, but that just seems to be used in the normal katakana contexts from what I've seen).