- trimester [trī mes′tər, trī′mes΄tər]n.[Fr trimestre < L trimestris, of three months < tri-, three + mensis, month: see MOON]1. a period or term of three months; specif., any of the three three-month periods of a human pregnancy2. in some colleges and universities, any of the three periods into which the academic year is divided
English World dictionary. V. Neufeldt. 2014.