It is unclear where the word originated. In China in the Classical period "tu-kin" referred to a group living to the south of the Altai massif. They might have been connected to the Huns. In Persian, "turk" was a slang for a barbarian. It isn't clear which informed the other. The word comes to Europe via Byzantine Greek Tourkos, Latin Turcus, and then Frenc Turc.