An archaic unit fraction variously defined as 1/200 (of an hour 
), 1/10 or 1/12 (of an inch 
), 1/12 (of a celestial body's angular diameter), or 1/60 (of an hour or degree).
Wells, D. The Penguin Dictionary of Curious and Interesting Numbers. New York: Penguin Books, p. 85, 1986.