(in many educational institutions) a division constituting half of the regular academic year, lasting typically from 15 to 18 weeks.
2.
(in German universities) a session, lasting about six months and including periods of recess.
Origin: 1820–30; < G < L sēmē(n)stris of six months duration < *sex-mēnstris, equiv. to sexsix+ mēns(is) month + -tris adj. suffix (perh. repr. an earlier *mens(i)-teros)
1827, from Ger. Semester, from L. semestris, in cursus semestris "course of six months," from semestris "of six months," from sex "six" + mensis "month."