Etymology
Advertisement
nail (n.)

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.

Related entries & more 
Advertisement
nail (v.)

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.

Related entries & more 
finger-nail (n.)
also fingernail, early 13c., from finger (n.) + nail (n.).
Related entries & more 
nail-clippers (n.)

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

Related entries & more 
nail-file (n.)

"small, flat, single-cut file for trimming the fingernails," by 1823, from nail (n.) + file (n.2).

Related entries & more 
Advertisement
nail-polish (n.)

"lacquer applied to the fingernail or toenails to protect and decorate," 1881, from nail (n.) + polish (n.).

Related entries & more 
nail-biter (n.)

"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.

Related entries & more 
toenail (n.)
also toe-nail, 1690s, from toe (n.) + nail (n.).
Related entries & more 
paronychia (n.)

"inflammation beside a fingernail," 1590s, from Latin, from Greek paronykhia "whitlow," from para- "beside" (see para- (1)) + onyx "nail" (see nail (n.)) + abstract noun ending -ia.

Related entries & more 
thumbnail (n.)
c. 1600, from thumb (n.) + nail (n.). Meaning "drawing or sketch of a small size" (though usually not literally the size of a thumbnail) is from 1852.
Related entries & more