'appui' originates from French, specifically the Old French word 'apui' (from the verb 'appuyer'), where the Vulgar Latin root *appodiare combined 'ad-' meaning 'to' and a root related to Latin 'podium/pos' meaning 'foot' or 'place'.

'appui' changed from Old French 'apui' (from verb forms like 'apuyer') and eventually became the modern French 'appui', adopted into English contexts as a loanword in technical or specialized usage.

Initially, it referred to a place or point for the foot (a physical support or foothold), and over time it broadened to mean any support, prop, or basis (including figurative uses).