-ian — one who, belonging to, skilled in (affix)

musician A2

/mjuˈzɪʃən/ A person who plays a musical instrument or composes music, especially as a job. M S

politician B1

/ˌpɑ.ləˈtɪʃ.ən/ A person who works in politics, especially one who has been elected to government. M S

comedian B1

/kəˈmiː.di.ən/ A performer whose job is to make people laugh, usually by telling jokes. M S

librarian B1

/laɪˈbɹɛɹ.i.ən/ A person who works in a library and helps people find books and information. M S

historian B1

/hɪˈstɔɹi.ən/ A person who studies or writes about history. M S