2. The Nail and the Clove; the Inch and the Ounce
The yard is lawfully divided (as was also the ell) into 4 quarters and 16 nails.
The hundredweight is divided into 4 quarters, 8 stones and 16 cloves or nails.
How did ‘Nail’ come to mean a sixteenth of a unit, length or weight?
The ‘New English Dictionary’ throws no light on the origin of this peculiarly English term. The only other general name I know for a sixteenth is the Indian ‘anna,’ the sixteenth of a rupee, of a crop, of a venture, &c.
The story of the Nail reaches back to the early history of weights and measures and is of philological as well as metrological interest. The half-cubit or span, the common handy measure in most parts of the world, is of 12 digits, while the foot is 16 digits and is still so divided in Italy and other southern countries. The digit is not only a middle-finger breadth, it is also a thumb-nail breadth; as the former it was in Greek dactylos, as the latter onyx, which became onkia in Southern Italy and gave rise to two Latin words, unguis for the actual finger-nail, uncia for the thumb-nail breadth equal to the digit and generally for a twelfth part. Hence a differentiation of meaning in the Romance languages.
Greek onyx, onkia
| Latin | unguis | uncia, thumb-nail breadth, ounce |
| Italian | unghia | oncia, last thumb-joint, ounce |
| Provençal | ounglo | ounço, finger-joint, knuckle, ounce |
| French | ongle | once, finger-joint (obs.), ounce |
| English | (nail) | unce, ynch |
When the Romans adopted the duodecimal or ‘uncial’ system they applied it to the foot, which was divided into either 12 or 16 parts both called unciæ; but to distinguish these they used two other words, digitus for the sixteenth and pollex, thumb, for the twelfth, the thumb-breadth.
In English ‘unce, ynch’ always meant the thumb-breadth 1/12 of a foot, ‘Nail,’ the thumb-nail breadth equal to the digit, being kept for the 1/16 foot. Thence ‘nail’ came to have the general sense of sixteenth and to be applied to that fraction of a 4-span yard, of a 5-span ell, of a bushel, of a hundredweight.