trafficyoudaoicibaDictYouDict[traffic 词源字典]
traffic: [16] The ultimate origins of traffic are not known. It was acquired from French traffique, which in turn was borrowed from Old Italian traffico, a derivative of the verb trafficare ‘trade’, but there the trail goes cold. It is generally assumed that the word’s first element goes back to the Latin prefix trāns- ‘across’.
[traffic etymology, traffic origin, 英语词源]
traffic (n.)youdaoicibaDictYouDict
c. 1500, "trade, commerce," from Middle French trafique (15c.), from Italian traffico (14c.), from trafficare "carry on trade," of uncertain origin, perhaps from a Vulgar Latin *transfricare "to rub across," from Latin trans- "across" (see trans-) + fricare "to rub" (see friction), with the original sense of the Italian verb being "touch repeatedly, handle."

Or the second element may be an unexplained alteration of Latin facere "to make, do." Klein suggests ultimate derivation of the Italian word from Arabic tafriq "distribution." Meaning "people and vehicles coming and going" first recorded 1825. Traffic jam is 1917, ousting earlier traffic block (1895). Traffic circle is from 1938.
traffic (v.)youdaoicibaDictYouDict
1540s, "to buy and sell," from traffic (n.) and preserving the original commercial sense. Related: Trafficked; trafficking; trafficker. The -k- is inserted to preserve the "k" sound of -c- before a suffix beginning in -i-, -y-, or -e- (compare picnic/picnicking, panic/panicky, shellacshellacked).