Relating to or characteristic of autumn; of or belonging to the autumn season.
From autumn + -ian (suffix forming adjectives meaning 'of or belonging to'). A somewhat archaic or poetic variant of autumnal, used primarily in older literature.
While 'autumnal' is common, 'autumnian' is so rare that many people mistake it for a made-up word—it's a beautiful archaic alternative that appears mostly in 19th-century poetry.
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