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.

Old English gnæt "gnat, midge, small flying insect," earlier gneat, from Proto-Germanic *gnattaz (source also of Low German gnatte, German Gnitze); perhaps literally "biting insect" and related to gnaw.

The gnatte is a litil fflye, and hatte culex he soukeþ blood and haþ in his mouþ a pipe, as hit were a pricke. And is a-countid a-mong volatiles and greueþ slepinge men wiþ noyse & wiþ bytinge and wakeþ hem of here reste. [Bartholomew Glanville, "De proprietatibus rerum," c. 1240, translated by John of Trevisa c. 1398 ]

Gnat-catcher, insectivorous bird of the U.S. woodlands, is from 1823.

1540s, from French erosion (16c.), from Latin erosionem (nominative erosio) "a gnawing away," noun of action from past-participle stem of erodere "to gnaw away, consume," from assimilated form of ex "away" (see ex-) + rodere "to gnaw" (see rodent). Related: Erosional.

1610s, "gnaw or eat away" (transitive), a back-formation from erosion, or else from French éroder, from Latin erodere "to gnaw away, consume," from assimilated form of ex "away" (see ex-) + rodere "to gnaw" (see rodent). Intransitive sense "become worn away" is by 1905. Related: Eroded; eroding. Originally of acids, ulcers, etc.; geological sense is from 1830.

"to bite gently; eat by gnawing off small bits," c. 1500, not found in Middle English; perhaps from Low German nibbeln "to nibble, gnaw," related to Middle Low German nibbelen, Middle Dutch knibbelen "to gnaw," source of Dutch knibbelen "to cavail, squabble." Related: Nibbled; nibbling.

c. 1400, corrosioun, from Old French corrosion and directly from Latin corrosionem (nominative corrosio), noun of action from past-participle stem of corrodere "to gnaw to bits, wear away," from assimilated form of com-, here perhaps an intensive prefix (see com-), + rodere "to gnaw" (see rodent).

late 14c., "to eat away, diminish or disintegrate (something) by gradually separating small bits of it," from Old French corroder (14c.) and directly from Latin corrodere "to gnaw to bits, wear away," from assimilated form of com-, here perhaps an intensive prefix (see com-), + rodere "to gnaw" (see rodent). Figurative use from 1630s. Related: Corroded; corroding.