trimester

noun

tri·​mes·​ter (ˌ)trī-ˈme-stər 

ˈtrī-ˌ

1

: a period of three or about three months

especially : any of three periods of approximately three months each into which a human pregnancy is divided

2

: one of three terms into which the academic year is sometimes divided

Did you know?

Semester, which comes from the Latin words for "six" and "month", has come to mean half an academic year when the year is divided into two segments. When an academic year is divided into three segments, each is called a trimester (which is usually a bit more accurate, since each segment often is close to three months in length). Some colleges operate on the "quarter" system, with the summer being the fourth quarter, but this just means that each quarter is basically a trimester. In a human pregnancy, a trimester is three months long, representing one-third of the nine months that a typical pregnancy lasts.

Examples of trimester in a Sentence

development in the first trimester

Recent Examples on the Web

While there are certainly a lot of dos and don'ts during pregnancy, lying on your stomach in the first trimester is not forbidden. —Elisa Cinelli, Parents, 2 July 2024

Medical experts say situations resulting in fetal death in the third trimester are rare — fewer than 1% of abortions in the U.S. occur after 21 weeks — and typically involve fatal fetal anomalies or life-threatening emergencies affecting the pregnant person. —Tribune News Service, The Mercury News, 28 June 2024

When Rupa Basu was pregnant with her second child, her body temperature felt out of control — particularly as her third trimester began in the summer of 2007. —Virginia Gewin, Vox, 30 May 2024

Dear Amy: Forty years ago, my wife was pregnant for one trimester. —Amy Dickinson, Detroit Free Press, 29 Feb. 2024

Word History

Etymology

French trimestre, from Latin trimestris of three months, from tri- + mensis month — more at moon

First Known Use

1821, in the meaning defined at sense 1

Phrases Containing trimester

• fourth trimester

Medical Definition

trimester

noun

tri·​mes·​ter (ˈ)trī-ˈmes-tər  ˈtrī-ˌ 

: a period of three or about three months

especially : any of three periods of approximately three months each into which a human pregnancy is divided