'avian' originates from Latin, specifically the word 'avis', where 'avis' meant 'bird'.

'avis' developed into Late Latin/Medieval Latin 'avianus' (meaning 'of or pertaining to birds'), which was later adopted into English as 'avian'.

Initially, it meant 'of or relating to birds' in Latin; over time it came to be used in English both as an adjective meaning 'relating to birds' and as a noun (plural 'avians') meaning 'birds' collectively.