nag (v.)youdaoicibaDictYouDict[nag 词源字典]
"annoy by scolding," 1828, originally a dialectal word meaning "to gnaw" (1825), probably ultimately from a Scandinavian source (compare Old Norse gnaga "to complain," literally "to bite, gnaw," dialectal Swedish and Norwegian nagga "to gnaw"), from Proto-Germanic *gnagan, related to Old English gnagan "to gnaw" (see gnaw). Related: Nagged; nagger; nagging.[nag etymology, nag origin, 英语词源]
nag (n.)youdaoicibaDictYouDict
"old horse," c. 1400, nagge "small riding horse," of unknown origin, perhaps related to Dutch negge, neg (but these are more recent than the English word), perhaps related in either case to imitative neigh. Term of abuse is a transferred sense, first recorded 1590s.