'peaceable' originates from Old French, specifically the word 'paisible', ultimately from Latin 'pax'/'pac-' where 'pax/pac-' meant 'peace' and the suffix '-able' (from Latin 'abilis') meant 'able to'.

'peaceable' changed from Old French 'paisible' into Middle English forms such as 'peysable' or 'peceable' and eventually became the modern English word 'peaceable'.

Initially, it meant 'able to be at peace' or 'characterized by peace'; over time it maintained that core sense and came to be used broadly for 'peaceful' or 'not inclined to fight' in modern English.