'duchy' originates from Old French, specifically the word 'duché', which in turn comes from Medieval Latin 'ducatus'; the Latin root 'dux' (genitive 'ducis') meant 'leader' and the suffix '-atus'/'-e' indicated an office or state.

'duchy' changed from Medieval Latin 'ducatus' into Old French 'duché' and eventually entered Middle English as 'duchy' (or forms like 'duchec'), becoming the modern English word 'duchy'.

Initially, it referred mainly to the office or jurisdiction of a duke ('the condition or office of a duke'), but over time the sense emphasizing the territory or domain ruled by a duke ('dukedom') became dominant.