dilation

noun

di·​la·​tion dī-ˈlā-shən 

plural dilations

: 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

Compared to white lights, low-intensity red ones minimizes pupil dilation, allowing better night vision; red light is also less disruptive to wildlife. —Alison Osius, Outside Online, 26 Nov. 2024

Quiros suggests bringing sunglasses with you to your appointment since dilation can make your eyes sensitive to light. —Korin Miller, Verywell Health, 14 Aug. 2024

Dimethyl sulfoxide infused in the vein has also been shown to cause dilation of the blood vessels, hypotension (low blood pressure), and chest pain. —Kirstyn Hill, Pharmd, Mph, Health, 22 Sep. 2024

So, upon signals of eating, the crossed nerve fibers lead not to salivation but heat responses, including sweat production and blood vessel dilation, which explains the facial flushing. —Beth Mole, Ars Technica, 10 Sep. 2024

Word History

First Known Use

circa 1598, in the meaning defined above

Phrases Containing dilation

• dilation and curettage
• dilation and extraction
• time dilation

Kids Definition

dilation

noun

di·​la·​tion dī-ˈlā-shən 

1

: the act of dilating : the state of being dilated : expansion

dilation of the pupils of the eyes

2

: the action of stretching or enlarging an organ or part of the body

Medical Definition

dilation

noun

di·​la·​tion dī-ˈlā-shən 

1

a

: 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