di·​la·​tion | \ dī-ˈlā-shən How to pronounce dilation (audio) \
plural dilations

Definition of dilation

: the act or action of enlarging, expanding, or widening : the state of being dilated: such as
a : the act or process of expanding (such as in extent or volume) … the dilation of palladium grains undergoing hydrogen absorption.— Frédéric Favier et al. The thermometer bulbs are subject to thermal and pressure dilation— Leslie A. Guildner
b : the act or action of stretching, widening, or enlarging an organ or part of the body dilation of the pupil with atropine Faced with threatening situations, the body responds with a sudden dilation of blood vessels.— Paul G. Donohue She has been treated with esophageal dilation, antacids and cimetidine …— David B. Adams This year in the United States, more than 200,000 balloon dilations of the coronary arteries will be done …— John Stone
c : the condition of being stretched or enlarged beyond normal dimensions : dilatation sense 1a chronic dilation of arterioles left ventricular dilation While the physiological cause of migraines is still unclear, researchers suspect that it involves the prolonged dilation of blood vessels in the brain.— Andrew Weil
d : an increase in duration of an event due to the effects of special relativity (see relativity sense 3a) However, if the Sun kept its same mass and were made smaller in circumference so its surface was closer to its center, then its gravity would be stronger, and correspondingly its gravitational time dilation—its warpage of time—would become larger.— Kip S. Thorne A related "time dilation" is caused by gravity: near a large mass, clocks tend to run slow.— Martin Rees

Examples of dilation in a Sentence

Recent Examples on the Web First, she would be given medication to induce dilation, and sent to her hotel room to wait. New York Times, 1 Aug. 2022 The woman’s doctor suggested ending the pregnancy via a dilation and evacuation rather than subjecting her patient to the anguish of a pointless labor, according to an affidavit the doctor filed in court, as reported by the Advocate. Monica Hesse, Washington Post, 22 July 2022 Add to that the agonizingly long stints of pupil dilation, and reindeer might experience something verging on mild glaucoma throughout much of their lives. Katherine J. Wu, The Atlantic, 28 June 2022 Most of the men and women who reported a response to the illusion also experienced pupil dilation. Manasee Wagh, Popular Mechanics, 13 June 2022 Testing this fuel will require Buzz to fly a series of missions, each one lasting only four minutes for him but, due to some clever time-dilation principles, a few years for those waiting patiently for him back on terra firma. Justin Changfilm Critic, Los Angeles Times, 13 June 2022 Nitric oxide is released from the interior of the artery, causing dilation. Bryant Stamford, The Courier-Journal, 12 May 2022 Also, a 2018 law banning a procedure generally used after the 14th week of pregnancy called dilation and evacuation remains subject to a legal challenge. Deborah Yetter, The Courier-Journal, 3 May 2022 The autonomic nervous system, which regulates things like heart rate, pupil dilation, body temperature, and digestion, can be split into two categories: the sympathetic nervous system and the parasympathetic nervous system. Jennifer Leman, Popular Mechanics, 28 Mar. 2022 See More

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

First Known Use of dilation

circa 1598, in the meaning defined above

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Time Traveler for dilation

Time Traveler

The first known use of dilation was circa 1598

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Dictionary Entries Near dilation

dilate on/upon


dilation and curettage

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Statistics for dilation

Last Updated

6 Aug 2022

Cite this Entry

“Dilation.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/dilation. Accessed 13 Aug. 2022.

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More Definitions for dilation


di·​la·​tion | \ dī-ˈlā-shən How to pronounce dilation (audio) \

Medical Definition of dilation

1a : the state of being dilated monitored cervical dilation
b : the act or action of stretching, widening, or enlarging an organ or part of the body dilation of the pupil with atropine
2 : the condition of being stretched or enlarged beyond normal dimensions : dilatation sense 1a chronic dilation of the arterioles left ventricular dilation

More from Merriam-Webster on dilation

Thesaurus: All synonyms and antonyms for dilation

Nglish: Translation of dilation for Spanish Speakers


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