Nag
early 19th century (originally dialect in the sense ‘gnaw’): perhaps of Scandinavian or Low German origin; compare with Norwegian and Swedish nagga ‘gnaw, irritate’ and Low German ( g)naggen ‘provoke’.
wiktionary
From Middle English nagg, nage, nagge(“horse, small riding horse, pony”), cognate with Dutch negge, neg(“horse”), German Nickel(“small horse”). Perhaps related to English neigh.
Probably from a North Germanic source; compare Swedish nagga(“to gnaw, grumble”), Danish nage, Icelandic nagga(“to complain”).
nag
etymonline
nag (v.)
1828, intransitive, "find fault constantly;" by 1840, intransitive, "annoy by continued scolding, pester with petty complaints," originally a dialectal word meaning "to gnaw" (1825, Halliwell), 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). As a noun, 1894, "act of nagging;" by 1925, "person who nags." Related: Nagged; nagger; nagging.
nag (n.)
"old horse," c. 1400, nagge "small riding horse, pony," a word 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. The term of abuse "a worthless person," often of a woman, is a transferred sense, first recorded 1590s. For "one who annoys by scolding" (by 1925) see nag (v.).
