'propitiatory' originates from Late Latin, specifically the word 'propitiatorius', where the root 'propiti-' (from Latin 'propitiare' / 'propitius') meant 'to make favorable, to appease'.

'propitiatorius' changed into Middle/Modern English forms (via Late Latin usage) and eventually became the modern English adjective 'propitiatory'.

Initially, it meant 'serving to appease or make favorable'; over time this core sense has been preserved and is retained in the modern meaning 'intended to appease or conciliate'.