Meaning of TRIMESTER in English

[noun] [C] - a three-month periodA trimester is any of the three three-month periods that a human pregnancy is divided into.Many women find the second trimester to be the easiest part of their pregnancy.(US) A trimester is any of the three-month periods into which the school or college year is sometimes divided.Many students arrange internships or work-study placements during the second trimester. Compare semester.

Cambridge English vocab.      Кембриджский английский словарь.