trimester

/ˌˈtraɪˌˈmɛstər/

/ˈtraɪmɛstə/

Other forms: trimesters

When something lasts for three months, you can say it lasts for a trimester. Each three-month period of pregnancy, for example, is one trimester.

A trimester is typically three months, including a trimester of human gestation (or the time pregnancy lasts), although sometimes it's a length of time divided into three equal parts. An academic calendar is usually split into two semesters, but when it's made up of three sections, each is a trimester. The Latin root of trimester is trimestris, "of three months," from tri-, "three," and mensis, "month."

Definitions of trimester

1. noun

   a period of three months; especially one of the three three-month periods into which human pregnancy is divided
   types:

   first trimester

   time period extending from the first day of the last menstrual period through 12 weeks of gestation

   second trimester

   time period extending from the 13th to the 27th week of gestation

   third trimester

   time period extending from the 28th week of gestation until delivery

   type of:

   period, period of time, time period

   an amount of time
2. noun

   one of three divisions of an academic year
   type of:

   academic session, academic term, school term, session

   the time during which a school holds classes