touryoudaoicibaDictYouDict[tour 词源字典]
tour: [14] Etymologically, a tour is a ‘circular movement’. The word comes via Old French tour from Latin tornus ‘lathe’, which also produced English turn. It was not used for a ‘journey of visits’ – literally a ‘circuitous journey’ – until the 17th century (the term grand tour, denoting a lengthy journey around western Europe formerly undertaken by fashionable young men, ostensibly for educational purposes, is first recorded in the mid-18th century, but the derivative tourist does not crop up until about 1800). Tournament [13] and tourney [13] both go back ultimately to a Vulgar Latin derivative of tornus, the underlying etymological notion being of the combatants ‘turning’ or wheeling round to face each other.

And tourniquet [17] probably comes from the same source.
=> tournament, tourniquet, turn[tour etymology, tour origin, 英语词源]
tour (n.)youdaoicibaDictYouDict
c. 1300, "a turn, a shift on duty," from Old French tor, tourn, tourn "a turn, trick, round, circuit, circumference," from torner, tourner "to turn" (see turn (v.)). Sense of "a continued ramble or excursion" is from 1640s. Tour de France as a bicycle race is recorded in English from 1916 (Tour de France Cycliste), distinguished from a motorcar race of the same name. The Grand Tour, a journey through France, Germany, Switzerland, and Italy formerly was the finishing touch in the education of a gentleman.
tour (v.)youdaoicibaDictYouDict
1746, "make a tour, travel about," from tour (n.). Related: Toured; touring.