A theologian is a person who studies religion as a subject of serious thought — what a religion teaches about God, why it teaches that, how its holy books should be read, how its ideas hold together or clash. The word points at study and argument, not at holiness or at leading worship. So a theologian is not the same as a priest, a pastor, a monk or a nun, though one person can be both: many theologians work in universities, write books, teach students, and some of them are not religious believers at all — you can study a religion carefully without following it. In practice, when English speakers say 'theologian' with no other word attached, the reader usually pictures a Christian one, simply because the word grew up inside European Christian scholarship; when the person studies another religion, speakers normally say so — 'a Muslim theologian', 'a Buddhist theologian'. The word carries a slightly weighty, bookish feeling. It is at home in a news article, a book review or a lecture, and would sound heavy in casual talk. Countable: a theologian, three theologians.