-ian Also -an.
Forming adjectives and nouns.
[Latin adjectival endings -anus, -ana, -anum, ‘of or belonging to something’.]
The original form was -an, as in urban (Latin urbanus, from urbs, city) and Roman (Latin Romanus, from Roma, Rome). However, many Latin words had an i before the ending (as in meridian, from Latin meridianum, noon; see -i-) and other examples in -ian come from French words in -ien (as in civilian, from Old French civilien) that are derived from Latin. As a result, the usual form is now -ian, though it is truncated to -an if the stem ends in a vowel.
One set is of adjectives that refer to places: Australian, Chicagoan, Indian, Kenyan, Malayan, Nebraskan, Parisian, Puerto Rican, Scandinavian, Tibetan, and so on. Some modify the stem: Glaswegian, Norwegian, Peruvian. Most can also be nouns that identify a person from that place.
Some adjectives derive from individuals' names and refer to a style or characteristic associated with that person. Many examples exist; new ones are created freely according to need. Some examples are Chestertonian, Clintonian, Hogarthian, Johnsonian, Nabokovian, and Orwellian. Some relate to periods of history named after monarchs: Edwardian, Elizabethan, Victorian.
Some personal names appear in adjectives and nouns that refer to systems of thought or belief, the founders of such systems, or their proponents: Copernican, Darwinian, Freudian, Hegelian, Lutheran. Others with related meanings are formed on a variety of stems: Episcopalian, Presbyterian, Puritan, Republican, utopian.
The endings also occur in nouns that denote someone who engages in, uses, or works with whatever is referenced by the stem: comedian, equestrian, historian, pedestrian, sacristan, thespian.