'autumnian' originates from Latin, specifically the word 'autumnus', with the adjectival suffix '-ian' ultimately from Late Latin '-ianus' meaning 'belonging to' or 'pertaining to'.

'autumnian' formed from English 'autumn' (which came from Latin 'autumnus' via Old French 'automne' and Middle English 'autumpne') combined with the suffix '-ian' (from Latin '-ianus'), yielding the modern adjective 'autumnian'.

Initially related to the Latin notion of 'autumn' or 'the season of harvest'; over time derivatives like 'autumnian' have come to mean more generally 'pertaining to or characteristic of autumn'.