se·mes·ter /səˈmɛstɚ/
  一學期,半學年,六個月的時間
  Se·mes·ter n.  A period of six months; especially, a term in a college or university which divides the year into two terms.
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  semester
       n 1: one of two divisions of an academic year
       2: half a year; a period of 6 months