trimester

noun

tri·​mes·​ter (ˌ)trī-ˈme-stər  ˈtrī-ˌme- 

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

As for when to host the get-together, during the third trimester works well, per Dr. Zechowy—about a month before your due date. —Melissa Willets, Parents, 11 Jan. 2025

Common milestones for announcements include the first prenatal appointment between 8 and 10 weeks, after the first trimester at 13 weeks, or after the first standard ultrasound exam at 18 to 22 weeks, according to Pampers. —Kevin Lynn, Newsweek, 6 Jan. 2025

The parties often take place during the third trimester when parents start to feel especially overwhelmed. —Lia Picard, New York Times, 26 Dec. 2024

In her caption over the video, Rae reflected on what working out can be like for pregnant women in the third trimester. —Charlotte Phillipp, People.com, 17 Dec. 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