"annoy by scolding," 1828, originally a dialectal word, probably ultimately from a Scand. source (cf. O.N. gnaga "to complain," lit. "to bite, gnaw," dial. Swed. and Norw. nagga "to gnaw") related to O.E. gnagan "to gnaw" (see gnaw).
"old horse," c.1400, nagge "small riding horse," of unknown origin, perhaps related to Du. negge, neg (but these are more recent than the Eng. word). Term of abuse is a transferred sense, first recorded 1598.