'autunian' originates from Medieval Latin/Latin via Old French and Middle English, ultimately from the Latin word 'autumnus' meaning 'autumn' (the season).

'autumnus' in Latin passed into Old French and Middle English as forms like 'autumpne'/'autumpn(e)' (and later 'autumn'), and adjectival formations using the suffix '-ian' produced 'autunian' as a less common variant alongside 'autumnal'.

Initially it indicated something 'of the autumn season' (often tied to harvest and maturity); over time it retained the general sense of 'pertaining to autumn' and is now used to mean 'autumnal' or 'characteristic of autumn'.