se·mes·ter 
(sə-mĕstər)
(sə-mĕstər)n.
One of two divisions of 15 to 18 weeks each of an academic year.
[German, from Latin (cursus) sēmēstris, (cursus) sēmēnstris, (course) of six months : sē-, six (from sex; see s(w)eks in the Appendix of Indo-European roots) + mēnsis, month; see mē-2 in the Appendix of Indo-European roots.]