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Dilation or Dilatation: Differences and Usage

Learning how to spell words in the English Language can be frustrating as the spelling and meanings of many words are so close that it makes them difficult to differentiate. For example, dilation and dilatation. Do we use them interchangeably? If not, then what is the difference?

The nouns “dilatation” and “dilation” are synonyms when describing the enlargement of a particular feature. However, in Merriam-Webster, “dilatation” can also indicate a stretching due to disease, overwork, or some abnormality. While “dilatation” is a much older word, the recent trend has favored “dilation.”

Biologists often use the terms interchangeably; however, dilatation does have a specific use when referring to the amplification of writing or speech. This article will discuss dilation and dilatation, their shared meaning, and attempt to tease out the subtle difference between them. 

What Does It Mean to Dilate Something?

Prior to the emergence of “dilation” or “dilatation,” there was the verb “dilate,” so it will help to have a better understanding of what it is to dilate something first.

Dilate is a verb meaning to spread out, become wide, or swell. For instance, when you see your eye doctor, they may dilate (make wider) the pupils of your eyes, which allows your eye doctor to check for any issues. 

While largely outdated, we can also use “dilate” as in to dilate on or upon something in the sense of commenting at length on a particular topic.

Dilation vs. Dilatation

Dilate (verb)Dilation (noun)Dilatation (noun)
To enlarge, spread out, or swell.
The act or state of being dilated (enlarged).
A dilated part or formation.
The act or state of being dilated (enlarged).
A dilated part or formation.

Also, something enlarged due to overwork, abnormal relaxation, or disease.
Also, to comment at length on a topic.The amplification of discourse — British English.The amplification of discourse — American English.

When comparing dilation versus dilatation, there appears to be little if any difference between them at first glance. When referring to organs, scientists and doctors often use them interchangeably.

However, in American English, we can use “dilatation” in a few additional contexts to refer to something stretched in a negative way or to the amplification of discourse. 

Where Dilation and Dilatation Overlap

We can describe either “dilation” or “dilatation” as an act of dilating or the state of being dilated. Dilation or dilatation refers to expansion or enlargement in all directions, like a bladder, an artery, or a balloon (source).

Both “dilation” and “dilatation” are noun forms of the verb “dilate.” We can use either term to refer to the stretching of a body part or organ.

As a count noun, Merriam-Webster states that the term “dilatation” can also describe the dilated part or formation of a hollow organ or vessel, and Collins Dictionary also applies this definition to “dilation” (source).

Collins also lists an additional surgical definition for “dilatation” as an enlargement that surgeons make in a bodily aperture or canal for treatment purposes.

Dilatation as an Abnormality

Like “dilation,” “dilatation” is the act or process of expansion, but it can also mean something stretched beyond its regular dimensions, such as the heart or stomach, through strain or abnormal relaxation.

Dilatation in Discourse

We can also use “dilatation” in a literary sense to indicate amplification of someone’s speech or writing. When you amplify your speech or a piece of writing, you add additional information. This usage actually appears in Middle English before its application to body parts.

Dilatation is a rhetorical device a writer uses to add further information to a sentence or embellish a story. This technique focuses the reader’s attention on an idea the writer fears they will miss (source).

Neither Merriam-Webster nor Collins Dictionary uses “dilation” in this sense. However, British English dictionaries like Lexico tend to use “dilation” to mean speaking or writing at length on that topic (source). 

Meanwhile,, now part of IXL Learning, headquartered in California with a local site in Canada, also lists “dilation” as a lengthy discussion on a specific topic (source). Over time, this distinction may break down.

Which Is More Common?

“Dilatation” is actually the much older word, dating to around 1400, whereas “dilation” emerged around the 1590s based on a misunderstanding of the Latin stem in “dilate” (source). For this reason, many doctors consider “dilatation” as the most etymologically sound choice.

However, a study published in the British Journal of Medicine found that “dilation” began to overtake “dilatation” beginning in 1996. This shift occurred first in American English, but British English has followed the same trend since (source). 

The Noun Suffixes -ation and -ion

“Dilate,” “dilatation,” and “dilation” all come from the Latin past participle stem of dilatare. A past participle normally expressed a completed action. In Latin, latus means broad, widespread, or extended, and dis means apart.

Dilatation and dilation both end with a noun suffix. A suffix is the group of letters we place at the end of a root word, thus forming a new word. We add the noun suffixes like -ation or -ion to a verb originating from Latin to change it to a noun.

“Dilation” emerged from the misunderstanding that the -ate in “dilate” was a Latin verbal suffix. Instead, it was part of the stem as “dilate” came from dilatare, where the -are is the verbal suffix.

Latin Noun Suffixes

Latin noun suffixes like -ation and ion alter a word to mean an act or process, the effect of an act or process, and a state or condition (source). Consider the following examples.

The eye doctor had to dilate my pupils.
The drops the doctor put in my eyes caused the dilation of my pupils.
I have to wear sunglasses due to the dilatation of my pupils.

Our teacher began to instruct us in science.
Our teacher’s instruction made the subject easier to understand.
Thanks to our teacher’s instruction I will not forget the information.

The doctor needed to excise my wart.
I remained awake during the excision of my wart.
Thanks to the excision the doctor performed, my wart is gone.

My stomach began to constrict.
The constriction of my stomach resulted in pain.
I am experiencing a great deal of pain thanks to the constriction of my stomach.

There are many more verbs that become nouns by adding -ion. Take note that -ion has related suffixes such as -tion, -ation, and -sion. They all refer to a process, action, and the outcome or result. Should you require a reference, you will find the Oxford English Dictionary invaluable.

Medical and Surgical Use of Dilation and Dilatation

To further understand the use of dilation in physiology and medicine, we will explore the various conditions to which doctors apply the word.

Coronary Dilation (Coronary Reflex)

Dilation affects the ventricles and atria of the heart, including the upper and lower chambers. The heart’s muscle will begin to stretch and become thinner, and this stretching causes the inside of the chambers to enlarge. As a result, coronary dilation prevents your heart from adequately pumping blood (source).


Also associated with the heart, vasodilation is a condition in which the luminal diameter of blood vessels widens.

Cervical Dilation

Dilation of the cervix occurs when a pregnant woman is ready to give birth to her child.

Esophageal Dilation

Esophageal dilation is a procedure to widen and stretch the esophagus. It is vital that your esophagus, the tube running from the mouth to the stomach, remain unconstricted. If it begins to narrow for some reason, your doctor may use this procedure to stretch the narrowed area back to its regular dimensions (source).

Pupillary Dilation (Ophthalmology)

Pupillary dilation occurs to allow the pupils of your eyes to admit more light. The muscles of the iris control the dilation. 

While pupillary dilation occurs naturally due to lighting conditions, certain drugs, such as decongestants, dilate the eyes. An eye doctor will use special drops made to dilate the pupils to check for disease. If you have a trip to the eye doctor planned, remember your sunglasses, as widened pupils let in a lot of light (source).

Aortic Dilatation vs. Aortic Dilation

Although we use both terms, for the most part, interchangeably, there is a distinct difference between aortic dilatation and aortic dilation. In American English, “dilation” typically only implies an expansion, whereas “dilatation” implies a pathological expansion. Let us first learn the function of our aorta. 

The Aorta

The aorta carries oxygenated blood throughout the circulatory system and is vital to survival. The aorta begins in the left ventricle of the heart and extends into the abdomen.

The aorta splits into the thoracic and abdominal aorta. The thoracic aorta comprises the following three parts: ascending aorta, the arch, and descending aorta.

Aortic Dilatation

Aortic dilatation refers to the dimension of the aorta, the diameter of which is related to a person’s age, sex, and body size. An aortic dilatation refers to the localized dilation of the aorta, and this is most common in elderly patients, although it does occur in younger patients less often (source).  

During the cardiac cycle, the middle aortic layer expands to propel the flow of blood forward. As we advance in age, the elasticity of the aorta declines and becomes stiff and weak. The descending aorta is then open to dilatation, and it begins the process of expansion.

For adults, aortic dilatation occurs when there is ascending aortic diameter over 1.57 inches (4 cm). 

Aneurysmal Dilatation

Aneurysmal dilatation occurs once that diameter reaches or surpasses 1.5 times the expected normal diameter of 1.97 inches (5 cm). This may lead to an aortic aneurysm.

According to Laplace’s Law (source), dilation causes possible vascular wall remodeling resulting from the increased tension on the walls, and this added tension may cause further dilatation of the aorta.

Doctors find most aneurysms in the tubular ascending aorta, generally in a tubular section or in the aortic root. Aortic dilatation is a silent disease but treatable. Regular doctor visits and vigilant attention to your health can prevent a tragedy. 

Dilation in Chemistry and Physics

Chemistry and physics, much like medicine and physiology, are scientific disciplines. As such, the meaning of dilation does not change, but its application does.

There is a process of dilation physicists and chemists refer to as thermal expansion.” Thermal expansion is a process that causes matter to change its shape, volume, area, or density as its temperature increases (source).

For more on chemistry and physics, you may wish to read our article “Exergonic vs. Exothermic: Different Energy Reactions.”

In both physics and math, “scale invariance” is a dilation. Scale invariance is an aspect of laws or objects that do not change according to length or another dimensional aspect, such as increasing or decreasing by a common factor. Dilation is the technical term for this phenomenon (source).

Time Dilation

Time dilation, in my opinion, is by far the most exciting subject in physics. As its name implies, it is related to time and how we perceive its passing. Time dilation occurs when we observe another person’s clock ticks at a slower rate than our own.

For instance, when given a physical duration, we can experience the duration of certain events to be subjectively longer than another. Take a glance at the second hand of a clock. You may notice the tick may appear to pause, making it appear longer than any successive ticks, even though you know each tick equals one.

Subjective Time Dilation

Subjective time dilation occurs when unexpected stimuli happen in a series of similar events — having the same features and duration — that may evoke an overestimation of subjective time. In this case, subjective refers to the modification of personal views, experiences, or backgrounds.

Virginie van Wassenhove and associates conducted an event-related functional MRI on the time dilation effect.

They showed each participant five static discs of equal duration and one disc of varying duration that loomed and receded. Subjects experienced subjective time dilation when the disc loomed but not when it receded (source).

This study shows our brains experience subjective time dilation differently than someone else. It is a self-referential experience. This article was written for

Dilation in Mathematics

In mathematics, dilation is a concept in geometry, metric space, operator theory, and scaling. The general definition of dilation is to resize something, generally to make it bigger. However, in mathematics, dilation means to make something smaller or larger (source).

Final Thoughts

Both “dilation” or “dilatation” can refer to the act of dilating or the state of being dilated. In medicine, they can refer to the expansion or enlargement of an organ or part of the body. 

However, “dilatation” usually has a more negative connotation of something stretched through overwork or abnormal relaxation. It can also refer to the amplification of discourse. In short, “dilatation” has other implications that “dilation” does not in American English.