The Greek obolos (originally meaning a copper nail), 1/6 of a drachm, acquired in Latin the sense of ‘half.’ When the drachma took the weight-sense of 60 grains, an obolus was 10 grains; but this was half a scruple, so it took a general sense of ‘half,’ and the halfpenny was latinised as an obolus.
Maille was the corresponding French word for halfpenny, being It. _medaglio_, Prov. _medaio_, akin not only to ‘medal’ but also to ‘metal,’ in which there seems to be a sense of ‘half’ of an alloy. Yet it became a weight of 1/4 ounce, perhaps from being half of the loth or half-ounce. And the Fr. _felin_, It. _ferlino_, probably corruptions of vierling or farthing, on becoming 1/4 of the _maille_, was 1/16 of the ounce. In the section on terms used in old land-measures I have shown the equivocal sense of words related to ‘ferling.’
Our Yard, from the influence of its French equivalents—_verge_, rod, and _vergée_, rood—became a quarter-acre, and then a quarter-hide.
The Drachm as a part of the Troy ounce, 1/8, became the dram as a part of the averdepois ounce, 1/16. As a measure it became 1/8 of a spirit pint.
The terms signifying 1/12, 1/16, 1/24 and some smaller fractions of weights or measures, show a development of meaning which will be given in the following sections.
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.