Diplomat

google

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early 19th century: from French diplomate, back-formation from diplomatique ‘diplomatic’, from Latin diploma (see diploma).

wiktionary

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From French diplomate, a back-formation from diplomatique(“diplomatic”), ultimately from Ancient Greek δίπλωμα(díplōma, “double-folded document”).

etymonline

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diplomat (n.)

"one skilled in diplomacy," 1813, from French diplomate, a back-formation from diplomatique "pertaining to diplomatics," from Modern Latin diplomaticus (see diplomatic) on model of aristocrate from aristocratique. Compare diplomatist.