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

Image: Meta Image: Meta Medication abortions in the first trimester of pregnancy can safely be done at home, according to the World Health Organization. —Mia Sato, The Verge, 24 Jan. 2025

Seventeen percent extended that cutoff to the first trimester of pregnancy, at around 12 weeks. —Nicole Blanchard, Idaho Statesman, 17 Jan. 2025

Implantation bleeding occurs in about 25% of pregnancies in the first trimester. —Anna Giorgi, Verywell Health, 4 Jan. 2025

Every pregnancy and person is different, and some may choose to don maternity clothes early in the first trimester, while others may prefer to wait until the second or third. —Casey Clark, Parents, 3 Jan. 2025

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