'propitiate' originates from Latin, specifically the verb 'propitiare' (and the adjective 'propitius'), where 'pro-' meant 'for' or 'in front of' and 'propitius' meant 'favourable' or 'inclined to favor'.

'propitiate' passed into English from Late Latin/Medieval Latin (e.g. 'propitiatus', past participle of 'propitiare') and entered Middle English usage, eventually becoming the modern English verb 'propitiate'.

Initially it was used in the sense of making someone (often a deity) favourable or inclined to favor; over time it has retained that basic sense but broadened to general acts of appeasing or conciliating people as well as gods.