We don't have synonyms for trimesters yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are trimester, trimeters and rimesters.
(n) :
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.
(n) :
A period of three months or about three months; (financial): quarter.
(n) :
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.
(n) :
A period of three months or about three months; (financial): quarter.