# trimester

/tɹaɪˈmɛstɝ/ (US) · /tɹˈaɪmɛstɐ/ (UK) · CEFR B2 · Noun

Source: https://englishreference.com/word/trimester
Updated: 2026-05-09

## Definition

one of the three periods that a pregnancy is divided into. It can also mean one of three terms in a school or university year.

For teachers: a period of three months, especially as a division of the duration of human pregnancy. Also refers to one of three terms into which an academic year is divided at some institutions.

## Examples

- She is currently in her second trimester of pregnancy.
- The university switched from a semester system to a trimester system to allow for a shorter summer break.
- During the first trimester, the developing embryo is particularly vulnerable to environmental factors, making prenatal care and nutrition critical during these initial twelve weeks.

## Usage notes

- Commonly used with ordinal numbers such as 'first', 'second', or 'third'.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.