'peaceably' originates from Modern English, specifically formed from the adjective 'peaceable' + the adverbial suffix '-ly', where 'peace' (Old English 'pēace') meant 'tranquility or absence of war'.

'peaceably' developed from Middle English forms such as 'peceably' (from Anglo-Norman/Old French), ultimately tracing back to Old French 'paisible' and Latin root 'pax / pac-' meaning 'peace'.

Initially it meant 'in a state or manner of peace' (or 'able to be at peace'), and over time it evolved into the adverb meaning 'in a peaceful manner' or 'without disturbance'.