Source : Webster's Revised Unabridged Dictionary (1913)

Semester \Se*mes"ter\, n. [G., from L. semestris half-yearly;
   sex six + mensis a month.]
   A period of six months; especially, a term in a college or
   uneversity which divides the year into two terms.

Source : WordNet®

semester
     n 1: one of two divisions of an academic year
     2: half a year; a period of 6 months