A French or archaic English spelling of 'ambassador,' referring to the highest-ranking official representative of one country sent to another country.
From Old French 'ambassadeur,' which comes from medieval Italian 'ambasciatore' (ambassador). The word's roots likely trace through Romance languages, possibly from Arabic 'ambaṣ' (messenger) or similar sources.
The 'deur' ending is pure French, and when English adopted this word, we eventually dropped the French spelling in favor of '-dor' in 'ambassador'—but in older documents you'll see 'ambassadeur' used by English writers wanting to sound fancy or diplomatic!
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