trimester
Americannoun
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a term or period of three months.
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one of the three approximately equal terms into which the year is divided by some colleges, schools, etc.
noun
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a period of three months
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(in some US and Canadian universities or schools) any of the three academic sessions
Other Word Forms
Derived Forms
Inflected Forms
Nouns
Etymology
Origin of trimester
1815–25; < French trimestre < Latin trimē ( n ) stris of three months, equivalent to tri- tri- + -mē ( n ) stris ( see semester)
Explanation
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."
Vocabulary lists containing trimester
Far from the Tree
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tri-
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tri (three)
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
See Examples For:
They combined those data with gut microbiome samples collected from 969 infants at 2, 6, and 12 months of age, along with microbiome samples from the infants' parents during the third trimester of pregnancy.
From Science Daily ● Jun. 2, 2026
Her next race was the Houston Marathon in January, when she was in her first trimester and won with a time of 2:24:17.
From BBC ● Apr. 21, 2026
But from 2021 to 2024, prenatal care starting in the first trimester declined to 75.5 percent.
From Salon ● Mar. 1, 2026
Late in her third trimester, doctors diagnosed her with placenta accreta, a potentially life-threatening condition in which the placenta grows too far into the wall of the uterus.
From The Wall Street Journal ● Dec. 28, 2025
By the time Grace realized what had happened, she was in the fifth day of her second trimester.
From "Far from the Tree" by Robin Benway
But there were increases in white-matter integrity - a measure of the health and quality of connections between brain regions - in the first and second trimesters, which returned to normal levels soon after birth.
From BBC ● Sep. 16, 2024
With training in complex family planning, she has experience seeing patients throughout all three trimesters of pregnancy.
From Salon ● Sep. 9, 2024
The analysis linked acetaminophen use in the second and third trimesters of pregnancy to modest but significant delays in early language development.
From Science Daily ● Jan. 3, 2024
Virginia law allows abortion during the first and second trimesters.
From Seattle Times ● Sep. 19, 2023
To qualify for education expense deductions, your expenditures can be made during academic periods that include quarters, trimesters, semesters or when coursework is provided during the summer.
From Encyclopedia.com ● Mar. 31, 2018
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
