The word uncia was Latin for a unit equal to 1/12 of another unit called the as. The words "inch" (1/12 of a foot) and "ounce" (originally 1/12 of a pound and still 1/12 of a "Troy pound," now used primarily to weigh precious metals) are derived from the word uncia.
Calcus, Half, Quarter, Scruple, Unit Fraction
Conway, J. H. and Guy, R. K. The Book of Numbers. New York: Springer-Verlag, p. 4, 1996.
Wells, D. The Penguin Dictionary of Curious and Interesting Numbers. New York: Penguin Books, p. 85, 1986.