Origins
The English word 'nail' is a remarkable case of dual meaning preserved across millennia. It refers both to the horny plate on a human finger or toe and to the pointed metal fastener — and this double sense is not a later metaphorical extension but an inheritance from Proto-Indo-European itself. The word descends from Old English 'næġl,' from Proto-Germanic *naglaz, from the PIE root *h₃nogʰ-, which already carried both meanings.
The evidence for this ancient duality comes from cognates across the Indo-European family. Latin 'unguis' (nail, claw) and its descendant French 'ongle' preserve the body-part sense. Greek 'onyx' (ὄνυξ) meant 'fingernail' or 'claw' before it came to name a gemstone whose pale bands were thought to resemble the translucent lunula at the base of a fingernail. Sanskrit 'nakha' meant 'nail, claw.' Irish 'ionga' (nail) descends from the same root. In Germanic, both senses survived side by side: German 'Nagel' means both fingernail and metal nail, as does Dutch 'nagel.'
The semantic logic connecting claw to fastener is not difficult to reconstruct. Early fastening pins were made from bone, horn, or thorns — materials that resembled claws or nails in shape and function. When metal pins replaced organic ones, the old name transferred naturally. The pointed, slightly curved shape of an animal claw is, after all, not far from a hand-forged iron nail.
Proto-Indo-European Roots
The phonological history shows the expected Germanic developments. PIE *h₃nogʰ- became Proto-Germanic *naglaz through regular sound changes: the initial laryngeal was lost, the vowel shifted, and the palatal stop became a velar. Old English 'næġl' (with the palatal 'ġ' before a front vowel) developed regularly into Middle English 'nail' as the palatal fricative was lost and the vowel lengthened in open syllables.
Nails as metal fasteners have an extraordinarily long history. The oldest known metal nails, made of bronze, date to roughly 3400 BCE in ancient Egypt. Iron nails appeared around 1000 BCE. Roman legions carried enormous quantities of iron nails for construction — the fortress at Inchtuthil in Scotland, abandoned by the Romans around 87 CE, yielded a hoard of nearly one million iron nails, deliberately buried to keep them from the local Caledonians. For most of human history, nails were hand-forged one at a time by blacksmiths, making them expensive enough that abandoned houses were sometimes burned down to recover their nails.
The word has generated a rich array of compounds and idioms. 'Hobnail' (a short nail with a large head, used on boot soles) comes from 'hob' in its sense of 'peg' or 'projection.' 'Nail-biter' for a tense situation dates from the mid-twentieth century. The phrase 'hit the nail on the head' (to identify something precisely) dates to the sixteenth century. 'Nail in the coffin' (a contributing factor toward failure) is attested from the late eighteenth century. 'Hard as nails' (tough, unsentimental) draws on the metal fastener's reputation for unyielding hardness.
Later History
The ancient unit of measurement called a 'nail' — equal to 2.25 inches or one-sixteenth of a yard — was used in the cloth trade from the medieval period onward. This measurement likely derived from the width of a thumb at the nail, connecting the body-part sense to a practical standard.
One of the more curious modern extensions is the 'nail' in fingernail care — the manicure and pedicure industry — which gave rise to 'nail salon,' 'nail polish,' and 'nail art,' all using the body-part sense. The existence of these parallel semantic fields — construction hardware and personal grooming — coexisting under one word testifies to the extraordinary staying power of the original PIE dual meaning. Five thousand years after PIE speakers used *h₃nogʰ- for both their claws and their fastening pegs, English speakers use 'nail' for both their fingertips and their toolboxes.