Forming adjectives and corresponding nouns.
[Originally from Latin words ending in -arius.]
Examples include agrarian (Latin ager, a field), relating to cultivated land or cultivation; antiquarian (Latin ante, before), relating to or dealing in antiques or rare books; disciplinarian (Latin disciplina, discipline), a person who promotes the orderly observance of rules. Others are centenarian, grammarian, librarian, proletarian, and veterinarian.
The most common use of this ending is to create adjectives from various English stems that refer to systems of thought or belief, or nouns for people who support or advocate them: authoritarian, contrarian (opposing or rejecting popular opinion or going against current practice), doctrinarian, egalitarian, fruitarian (a person who lives on fruit only), humanitarian, libertarian, sectarian, totalitarian, Unitarian, vegetarian.