From Gaulish Celtic ambactos (servant), through Latin and Italian, to French ambassade — a word Julius Caesar recorded from the Gauls
The official residence or office of an ambassador in a foreign country, or the diplomatic mission itself
From Middle French 'ambassade' (earlier 'embassade'), from Old Italian 'ambasciata' meaning a mission or message, from Medieval Latin 'ambactia' (a mission, service), from the Gaulish Celtic root 'ambactos' meaning servant or vassal. Caesar recorded this Celtic word in his account of Gaul, describing the ambacti as dependents or retainers of Gaulish chiefs. The word traveled from Celtic through Latin, Italian, and French before reaching
Julius Caesar himself recorded the Gaulish word ambactos in De Bello Gallico, describing it as the Celtic term for retainers who owed service to their chief. This Celtic word survived the fall of Rome, the rise of Romance languages, and a thousand years of linguistic change to end up naming the buildings where modern diplomats work.