-ian +

(Latin: suffix form of -an from -ianus, a modifier of the main word to which it is attached: belonging to, coming from, being involved in, or being like something)

Appearing in such words as comedian, egalitarian, Bostonian, Italian, Smithsonian, mathematician, Alabamian, Californian, Arizonian, and Canadian. It is attached to the root of common or proper nouns with the meanings "of, pertaining to, from", or "like" the proper name appearing in the stem.

—Based on information from The Barnhart Dictionary of Etymology,
Edited by Robert K. Barnhart, The H.W. Wilson Company, 1988.