'duotone' originates from Latin and Greek elements, specifically the Latin 'duo' and the Greek word 'tonos', where 'duo' meant 'two' and 'tonos' meant 'tone' or 'stretch (pitch).'

'duotone' was formed in modern English (20th century) by combining the Latin-derived prefix 'duo-' ('two') with English 'tone' (from Greek 'tonos' via Latin 'tonus' and Old French), resulting in the compound 'duotone.'

Initially it referred specifically to printing and photographic techniques using two inks or tones; over time it has come to refer both to the technique/process and to any image or design rendered in two tones.