NOUN (2)

1. one of two divisions of an academic year;

2. half a year; a period of 6 months;

The Collaborative International Dictionary of English v.0.48:

Semester \Se*mes"ter\ (s[-e]*m[e^]s"t[~e]r), n. [G., from L.
   semestris half-yearly; sex six + mensis a month.]
   A period of six months; especially, a term in a college or
   university which divides the year into two terms.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "semester":
   abundant year, academic year, annum, bissextile year,
   calendar month, calendar year, century, common year, day, decade,
   decennary, decennium, defective year, fiscal year, fortnight, hour,
   leap year, lunar month, lunar year, lunation, luster, lustrum,
   man-hour, microsecond, millennium, millisecond, minute, moment,
   month, moon, quarter, quinquennium, regular year, second, session,
   sidereal year, solar year, sun, term, trimester, twelvemonth, week,
   weekday, year