'autochthon' originates from Ancient Greek, specifically the word 'autochthōn', where 'autos' meant 'self' and 'chthōn' meant 'earth' or 'soil'.

'autochthōn' passed into Late Latin/Neo-Latin as 'autochthon' and was borrowed into English (chiefly in scholarly and literary contexts) with the sense 'native, sprung from the soil'.

Initially it referred literally to someone 'sprung from the earth' in Greek myth and came to be used more generally for 'an indigenous/native person or organism' in modern usage.