trader (n.)youdaoicibaDictYouDict[trader 词源字典]
"dealer, trafficker, one engaged in commerce," 1580s, agent noun from trade (v.).[trader etymology, trader origin, 英语词源]
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).