in Greek and Roman mythology, "water nymph," one of the female deities presiding over springs and streams, c. 1600, from Latin Nais, Naias (genitive naiadis), from Greek Naias (plural Naiades) "river nymph," from naiein "to flow," from PIE *naw-yo-, suffixed form of *(s)nau- "to swim, flow, let flow" (from PIE root *sna- "to swim"). Dryden used the Latin singular form Nais, and the plural Naiades is attested in English from late 14c.

"ingenuous, artless, natural," 1590s, from French naïf, literally "naive" (see naive). The masculine form of the French word, but used in English without reference to gender. As a noun, "natural, artless, naive person," first attested 1893, from French, where Old French naif also meant "native inhabitant; simpleton, natural fool."

Old English negel "tapering metal pin," nægl "fingernail (handnægl), toenail," from Proto-Germanic *naglaz (source also of Old Norse nagl "fingernail," nagli "metal nail;" Old Saxon and Old High German nagel, Old Frisian neil, Middle Dutch naghel, Dutch nagel, German Nagel "fingernail; small metal spike"), from PIE root *(o)nogh "nail of the finger or toe" (source also of Greek onyx "claw, fingernail;" Latin unguis "fingernail, claw;" Old Church Slavonic noga "foot," noguti "fingernail, claw;" Lithuanian naga "hoof," nagutis "fingernail;" Old Irish ingen, Old Welsh eguin "fingernail, claw").

The "fingernail" sense seems to be the original one, but many figurative uses are from the "small metal spike" sense: hard as nails is from 1828. To hit the nail on the head "say or do just the right thing" is by 1520s; in Middle English driven in the nail (c. 1400) was "to drive home one's point, clinch an argument," and smiten the nail on the hed was "tell the exact truth" (mid-15c.). Phrase on the nail "on the spot, exactly" is from 1590s, of obscure origin; OED says it is not certain it belongs to this sense of nail.

As a unit of English cloth measure (about 2 1/4 inches) from late 14c.; perhaps from a nail being used to mark that length on the end of a yardstick.

Old English næglian "to fix or fasten (something) onto (something else) with nails," from Proto-Germanic *ganaglijan (source also of Old Saxon neglian, Old Norse negla, Old High German negilen, German nageln, Gothic ganagljan "to nail"), from the root of nail (n.). Related: Nailed; nailing. The colloquial meaning "secure, succeed in catching or getting hold of (someone or something)" is by 1760; hence "to arrest" (by 1930). Meaning "to succeed in hitting" is from 1886. To nail down "to fix down with nails" is from 1660s.

"worrisome or suspenseful experience," by 1999, perhaps originally in reference to close games in sports, from the notion of biting one's fingernails as a sign of anxiety (attested from 1570s); see nail (n.) + bite (v.). Nail-biting (n.) is from 1805; nail-biter as "person who habitually or compulsively bites his fingernails" is by 1856.

"hand-tool used to trim the fingernails and toenails," 1890, from nail (n.) + clipper (n.).

"workshop where nails are made," 1798, from nail (n.) + -ery or from nailer "one who makes nails" (mid-15c.) + -y (1).

"small, flat, single-cut file for trimming the fingernails," by 1819, from nail (n.) + file (n.2).

1881, originally "substance used to buff the nails." From nail (n.) + polish (n.). The sense of "liquid nail varnish" is 1895.

"birth, origin," late 15c. (Caxton), from French naissance "birth, parentage, place of origin" (12c.), present participle of naître, from Gallo-Roman *nascere, from Latin nasci "be born" (see genus).