From Latin 'uncia' (a twelfth part) — same word that produced 'ounce,' preserving the Roman base-12 system.
Definition
A unit of length equal to one-twelfth of a foot (2.54 centimeters).
The Full Story
LatinOld Englishwell-attested
From OldEnglish 'ynce,' borrowed from Latin 'ūncia' (a twelfth part), from 'ūnus' (one), from PIE *óynos (one). The Latin word 'ūncia' meant any twelfth — it wasone-twelfth of a Roman foot ('pēs,' approximately 29.6 cm) and one-twelfth of a Roman pound ('lībra,' approximately 327 grams). This dual application producedtwo
root *óynos (one) is also the ancestor of Latin 'ūnus' (one), 'ūnicus' (unique), 'ūniō' (union, oneness — also 'a single large pearl,' whence 'onion' via Old French), 'ūniversus' (
into one, universal), and 'ūniformis' (uniform). Through Germanic *ainaz it gave Old English 'ān' (one), whence modern 'one,' 'an,' 'a,' 'alone,' 'atone' (at-one), 'any,' and 'none.' The humble inch thus connects to the deepest concept in counting — the number one — through an ancient Roman system of twelfths that also gave us the ounce. Key roots: ūncia (Latin: "a twelfth part"), *óynos (Proto-Indo-European: "one").