Negotiator

wiktionary

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Borrowed from Latin negōtiātor(“merchant, banker”), equivalent to negotiate +‎ -ator

etymonline

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negotiator (n.)

1590s, "businessman" (a sense now obsolete); c. 1600, "one who carries on negotiations, one who treats with others as either principal or agent;" from Latin negotiator "one who carries on business by wholesale," from negotiatus, past participle of negotiari "carry on business, do business" (see negotiation).