As nouns the difference between mester and semester
is that mester is obsolete form of nodot=yes|lang=en (employment, trade while semester is half of a school year or academic year such as fall or spring semester.
is that sester is (history) 1 as a liquid measure for honey and wine between 24 and 32 ounces 2 a dry measure for grain maybe equal to 12 bushels while mester is (employment, trade).