Definition from Wiktionary, the free dictionary
See also Trimester
trimester (plural trimesters)
- A period of three months or about three months.
- She is in the second trimester of her first pregnancy.
- One of the terms of an academic year in those learning institutions that divide their teaching in three roughly equal terms, each about three months long. Compare semester.
- The school operates on a trimester schedule.
Coordinate terms 
- (term of academic year): academic year
- (term of academic year): term
period of three months
term of academic year