dilation

American  

[dahy-ley-shuhn, dih-] / daɪˈleɪ ʃən, dɪ- /

noun

1. the act of dilating; state of being dilated.

2. dilatation.

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dilation Scientific  

/ dī-lā′shən,dĭ- /

1. The widening or stretching of an opening or a hollow structure in the body.

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Other Word Forms

• nondilation
  noun
• overdilation
  noun
• self-dilation
  noun

Etymology

Origin of dilation

First recorded in 1590–1600; dilate + -ion

Explanation

Dilation is expansion, usually of an opening such as the pupil. When that happens, your eyes look black and the light comes streaming in. Grab your sunglasses! The word dilation is the noun form of dilate, "to make wider.” Dilation often refers to what happens when a woman goes into labor, and her cervix dilates to let the baby through. Dilation is also used for writing or speech that expands on a topic. Here’s a dilation: funny thing is that the -ate ending of dilate is not a suffix but part of the word, so it should really be dilatation, but no one says it that way.

Example Sentences

Caffeine temporarily shrinks blood vessels and less dilation means less visible swelling.

From BBC • Feb. 16, 2026

Not only do we tend to mirror each other’s movements, postures, facial expressions and gestures; we also uncannily sync up our heart rates, blood pressure, pupil dilation and hormonal activity.

From The Wall Street Journal • Jan. 22, 2026

Time itself passes differently at such distances -- a phenomenon known as cosmological time dilation.

From Science Daily • Nov. 7, 2025

In the 1990s, anti-abortion activists got a leaked copy of a paper that was presented at the annual conference of the National Abortion Federation describing a procedure called dilation and extraction.

From Slate • Sep. 17, 2024

You become compressed in the direction of motion, your mass increases, and time, as you experience it, slows down, a breathtaking consequence of traveling close to the speed of light called time dilation.

From "Cosmos" by Carl Sagan