'antimer' (plural 'antimeres') originates from Greek, specifically the word 'antímeros', where 'anti-' meant 'opposite' or 'against' and 'meros' meant 'part'.

'antímeros' in Greek passed into New/Medieval Latin as 'antimerus' and was borrowed into English in the form 'antimer' (plural 'antimeres').

Initially it meant 'an opposite part' in the literal Greek sense, and it has retained that core meaning as 'a corresponding/opposite part' in modern anatomical usage.