tri ‧ mes ‧ ter /trɪˈmestə $ traɪˈmestər/ BrE AmE noun [countable]
[ Date: 1800-1900 ; Language: French ; Origin: trimestre , from Latin trimestris , from tri- 'three' + mensis 'month' ]
1 . American English one of three periods of equal length that the school year is divided into SYN term British English
2 . one of the three-month periods of ↑ pregnancy