'medievalism' originates from Modern English formation: the adjective 'medieval' + the suffix '-ism'. 'Medieval' ultimately comes from Medieval Latin 'medievalis', where 'medium' meant 'middle' and 'aevum' (or 'aevum') meant 'age'. The suffix '-ism' (from Greek via Latin and French) denotes a system, practice, or ideology.

'medieval' derived from Medieval Latin 'medievalis' (from 'medium aevum' meaning 'middle age'); that adjective entered later English usage. The noun 'medievalism' was formed in Modern English (notably used from the 19th century) by adding the productive suffix '-ism' to 'medieval', producing the term for the revival/interest in the Middle Ages.

Initially the root elements referred specifically to the 'middle age(s)'; over time the compound 'medievalism' came to mean not just 'relating to the Middle Ages' but a cultural movement, revival, or approach that studies, imitates, or idealizes medieval life and aesthetics.