a suffix forming personal nouns corresponding to Latin adjectives ending in -ārius or English adjectives or nouns ending in -ary (librarian; proletarian; Rotarian; seminarian; sexagenarian; veterinarian); subsequently productive in English with other Latinate stems, forming nouns denoting a person who supports, advocates, or practices a doctrine, theory, or set of principles associated with the base word: authoritarian; establishmentarian; totalitarian; vegetarian.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
British Dictionary definitions for -arian
suffix forming nouns
indicating a person or thing that advocates, believes, or is associated with somethingvegetarian; millenarian; librarian
Word Origin for -arian
from Latin -ārius -ary + -an
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012