Semester (4)
I believe the answer is:
term
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">semester</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for term that I've seen before include "Word; school session" , "Fixed period or special word" , "Limit - school time" , "Limited period; school session" , "Spell - word" .)