'antichthones' originates from Greek, specifically the word 'antichthōnēs', where 'anti-' meant 'opposite' and 'chthōn' meant 'earth'.

'antichthones' changed from Ancient Greek 'antichthōn/antichthōnēs' and entered learned Latin and medieval writings (as 'antichthon'/'antichthones'), later appearing in English texts as a borrowed classical/learned term.

Initially, it meant 'people dwelling on the opposite side of the earth' (or the notion of an 'opposite earth'); over time it retained that rare, classical sense and was also used to denote the philosophical/astronomical idea of a 'counter-earth'.