'antagony' originates from Greek/Medieval Latin, specifically the Greek element 'antagōnia' (from Greek 'antí-' meaning 'against' + 'agṓn/ἀγών' meaning 'contest' or 'struggle').

'antagony' later appeared in Medieval Latin/early modern English forms (e.g. Medieval Latin 'antagonia') and was used in English texts with senses of contest or opposition, eventually surviving only as a rare or archaic noun in modern English.

Initially, it meant 'a contest or struggle (a contesting against)', but over time it narrowed to senses of 'opposition' or 'hostility' and then became rare/archaic in modern usage.