'diptych' originates from Middle English and Medieval Latin, specifically Medieval Latin 'diptycha' (plural of 'diptychum'), where 'di-' meant 'two' and 'ptyche' (from Greek) meant 'fold' or 'layer'.

'diptych' changed from Greek 'diptychos' (δίπτυχος) to Latin/Medieval Latin 'diptychum'/'diptycha', then entered Middle English as 'diptych' and remained in English with that form.

Initially it meant 'a writing tablet folded in two' (a two-leaved tablet), but over time it evolved into the modern primary sense of 'a two-panel artwork' and more broadly 'a pair of related works'.