A traditional unit of volume for liquids. The tertian, like the tierce (see below) takes its name from the Latin for 1/3. It equals 1/3 tun, which is 2 tierces or 84 U.S. gallons (about 318 liters)
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}