'antimedievalism' originates as a modern English compound combining the prefix 'anti-' (from Greek anti- meaning 'against') with 'medieval' (from Medieval Latin 'medium aevum' meaning 'the middle ages') and the suffix '-ism' (from Greek/Latin, indicating a doctrine or system).

'medieval' comes from Medieval Latin 'medium aevum' ('middle age'); English 'medieval' developed in the 17th–19th centuries to refer to the Middle Ages. 'Antimedievalism' is a later English formation (19th–20th century onward) creating an ideological noun by adding 'anti-' and '-ism' to 'medieval.'

Initially compounds with 'anti-' plus historical-period names simply marked opposition to that period; over time 'antimedievalism' has come to mean not only opposition to the Middle Ages themselves but specifically opposition to the modern revival, influence, or valorization of medieval styles and values.