'azygos' originates from Greek, specifically the word 'ἀζύγος' (transliterated 'azygos'), where the prefix 'a-' meant 'not' and 'zygos' meant 'yoked' or 'paired'.

'azygos' came into New Latin/medical usage from the Ancient Greek 'ἀζύγος' and was adopted into English medical terminology without substantial change in form.

Initially it meant 'not yoked' or 'unpaired' in Greek; over time the meaning has been retained but specialized in modern English to describe unpaired anatomical structures (notably the azygos vein).