Semester

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early 19th century: from German Semester, from Latin semestris ‘six-monthly’, from sex ‘six’ + mensis ‘month’.

wiktionary

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From German Semester, from New Latin sēmestris(“lasting six months”), from sex(“six”) + mēnsis(“month”).

etymonline

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semester (n.)

1827, from German Semester "half-year course in a university," from Latin semestris, in cursus semestris "course of six months," from semestris, semenstris "of six months, lasting six months, half-yearly, semi-annual," from sex "six" (see six) + mensis "month" (see moon (n.)). Related: Semestral; semestrial.