Synonyms for Semester:

n.

midterm, grade, start back, summer holiday, long vacation, half-term, open house, spring break, midterm break. point of time (noun)
decade, epoch, minute, week, millisecond, hour, age, century, microsecond, year, lifetime, generation, month, millennium, time, day, term, era, second.
quarter (noun)
term.
term (noun)
six-month period, time, four and one-half months, eighteen weeks.
time period (noun)
term.

Other synonyms:

midterm, spring break, summer holiday, half-term, midterm break, long vacation. open house, start back. grade. Other relevant words:
grade, midterm.