An alternate name for the baker's dozen, a traditional unit of quantity equal to 13. This name reflects the long-standing association of the number 13 with bad luck or evil
Russ Rowlett (Director), How Many? A Dictionary of Units of Measurement, Center for Mathematics and Science Education University of North Carolina, USA 2005. http://www.unc.edu/~rowlett/units/dictA.html, (Unit of Meas and Covr Factors - Amer) {608}