'antimediaeval' originates from Modern English, formed from the prefix 'anti-' (from Greek 'anti-' meaning 'against') and 'mediaeval' from Medieval Latin 'mediaevus', where 'medius' meant 'middle' and 'aevum' meant 'age'.

'mediaeval' comes from Medieval Latin 'mediaevus' (from 'medius' + 'aevum'), passed into Middle English as 'mediæval' and later 'medieval'; the adjective 'antimediaeval' is formed by combining the prefix 'anti-' with this word to indicate opposition to medieval or mediaeval characteristics.

Initially it would have the literal sense 'against the Middle Ages' or 'against medieval things'; over time it has been used more specifically to describe opposition to medieval styles, institutions, or the 19th/20th-century revivals and nostalgias termed 'medievalism'.