late 14c., "one of the two chief magistrates in the Roman republic," from Old French consule and directly from Latin consul "magistrate in ancient Rome," probably originally "one who consults the Senate," from consulere "to deliberate, take counsel" (see consultation).
Its modern sense of "agent appointed by a sovereign state to reside in a foreign place to protect the interests of its citizens and commerce there" began with use of the word as appellation of a representative chosen by a community of merchants living in a foreign country (c. 1600), an extended sense that developed 13c. in the Spanish form of the word.
In French history it refers to the title given to the three magistrates of the republic after the dissolution of the Directory in 1799. Old English glossed the Latin word with gercynig, "year-king, king whose authority lasted a year," as the closest notion of it they could form in their language (Ælfric's vocabulary also has it as gerefa "reeve," a high-ranking king's officer).