tri·​mes·​ter | \ (ˌ)trī-ˈme-stər How to pronounce trimester (audio) , ˈtrī-ˌ\

Definition of trimester

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

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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

Mexican political and economic analyst Macario Schettino wrote recently for the newspaper El Financiero that unless trends change, investment could fall 5% in the first trimester and possibly remain at similar levels throughout 2019. Peter Orsi, The Seattle Times, "At US-Mexico CEO summit, leaders optimistic amid uncertainty," 12 Apr. 2019 The restrictions just meant delayed care and increased the number of second-trimester abortions. Glamour, "Abortion Bans Are a Call to Action—Not a Reason to Give Up," 29 Mar. 2019 Like many women in their third trimester, (myself included) sometimes towards the end that engagement ring and wedding band just won’t fit! Erica Gonzales, Harper's BAZAAR, "Meghan Markle Stepped Out without Her Engagement Ring with Prince Harry," 11 Mar. 2019 Christina Spirig, a pole-dancing instructor, continued her sport up until her last trimester. Rebecca Flood, Fox News, "Pole-dancing mom in Switzerland credits hobby with helping her recover from pregnancy," 30 Aug. 2018 Pippa recently opened up about her first trimester in her latest column for the U.K. supermarket monthly Waitrose Kitchen magazine. Erin Hill,, "Pregnant Pippa Middleton (in Baby Blue!) Arrives at Her Nephew Prince Louis' Christening," 9 July 2018 During the first trimester of pregnancy, your blood volume increases, so your kidneys have to process extra fluid, the Mayo Clinic explains. Korin Miller, SELF, "7 Ways to Make Sleep More Comfortable When You’re Pregnant," 31 Jan. 2019 The Bump reports that, according to the American Congress of Obstetricians and Gynocologists, women are generally safe to use air travel into their third trimester, but not after 36 weeks. Amy Mackelden, Harper's BAZAAR, "Meghan Markle Arrives in Morocco Wearing the Most Stunning Valentino Cape Dress," 23 Feb. 2019 But after the capital legalized first-trimester abortions on demand in 2007, over half the states passed right-to-life bills declaring that life begins at conception. Fox News, "Mexico City bans use of attractive models during city events," 19 Aug. 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'trimester.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of trimester

1821, in the meaning defined at sense 1

History and Etymology for trimester

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

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Statistics for trimester

Last Updated

28 Apr 2019

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The first known use of trimester was in 1821

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English Language Learners Definition of trimester

: a period of three months especially : one of three periods into which a woman's pregnancy is often divided
US : one of three periods into which an academic year is sometimes divided


tri·​mes·​ter | \ (ˈ)trī-ˈmes-tər How to pronounce trimester (audio) , ˈtrī-ˌ How to pronounce trimester (audio) \

Medical Definition of trimester

: 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

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Rhyming Dictionary: Words that rhyme with trimester

Spanish Central: Translation of trimester

Comments on trimester

What made you want to look up trimester? Please tell us where you read or heard it (including the quote, if possible).


a sum of money that is sent as a payment

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