di·​am·​e·​ter | \ dī-ˈa-mə-tər How to pronounce diameter (audio) \

Definition of diameter

1 mathematics : a chord (see chord entry 3 sense 2) passing through the center of a figure or body
2 mathematics : the length of a straight line through the center of an object or space the diameter of a circle dug a hole nearly four feet in diameter
3 physics : a unit of enlargement used with a number to indicate magnification by a lens or optical system an object one millimeter wide magnified 40 diameters appears 40 millimeters wide

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Other Words from diameter

diametral \ dī-​ˈa-​mə-​trəl How to pronounce diametral (audio) \ adjective

Examples of diameter in a Sentence

The dotted line indicates the diameter of the circle. What is the diameter of the tree trunk? Dig a hole that's two feet deep and three feet in diameter.
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Recent Examples on the Web

The area, an inch in diameter, also contained a marked concentration of blood vessels. Katherine Foxhall, Time, "How A Nurse With a Hole in Her Skull Changed The Medical History of Migraines," 18 June 2019 Large hail, up to 2 inches in diameter, could cause damage to cars and homes in the area. Kirk Mitchell, The Denver Post, "Denver weather: Marginal risk of egg-sized hail, heavy rain and wind gusts up to 60 mph over Front Range," 17 June 2019 The non-venomous snake measured about a foot long and a quarter-inch in diameter, officials said. USA TODAY, "Retired monkeys, freeze-dried blood, ‘Hidden Figures Way’: News from around our 50 states," 14 June 2019 The researchers note that the rings, which are between 2.6 and 3.6 centimeters in diameter, were deliberately put into the storage pit. Fox News, "World’s first 'Cheerios' found: 3,000-year-old ‘cereal rings’ discovered in ancient fort," 11 June 2019 According to Fidler, the new drainage system is essentially a large pipe in the shape of an L that will be between 18 and 36 inches in diameter. Libby Solomon, baltimoresun.com, "Stoneleigh stormwater drainage project to get started this summer, county says," 10 June 2019 The human hair averages between 50 and 70 microns in diameter. Stephen Leahy, National Geographic, "Microplastics are raining down from the sky," 15 Apr. 2019 Blood vessels in the brain are tiny and fragile, about 2 to 3 millimeters in diameter and of thinner composition than other vessels, with less lining. Hillary Davis, latimes.com, "Stroke survivors of all ages celebrate and thrive at gathering in Fountain Valley," 6 June 2019 The object is roughly 40 meters in diameter, according to the ESA. Michelle Lou, CNN, "The asteroid supposedly the size of a football field that people are freaking out about? Don't sweat it," 6 June 2019

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

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First Known Use of diameter

14th century, in the meaning defined at sense 1

History and Etymology for diameter

Middle English diametre, from Middle French, from Latin diametros, from Greek, from dia- + metron measure — more at measure

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Statistics for diameter

Last Updated

24 Jun 2019

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Time Traveler for diameter

The first known use of diameter was in the 14th century

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English Language Learners Definition of diameter

: a straight line from one side of something (such as a circle) to the other side that passes through the center point
: the distance through the center of something from one side to the other


di·​am·​e·​ter | \ dī-ˈa-mə-tər How to pronounce diameter (audio) \

Kids Definition of diameter

1 : a straight line that runs from one side of a figure and passes through the center Measure the diameter of the circle.
2 : the distance through the center of an object from one side to the other : thickness the diameter of a tree trunk


di·​am·​e·​ter | \ dī-ˈam-ət-ər How to pronounce diameter (audio) \

Medical Definition of diameter

1 : a unit of magnification for an optical instrument equal to the number of times the linear dimensions of an object are apparently increased a microscope magnifying 60 diameters
2 : one of the maximal breadths of a part of the body the transverse diameter of the inlet of the pelvis

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More from Merriam-Webster on diameter

Rhyming Dictionary: Words that rhyme with diameter

Spanish Central: Translation of diameter

Nglish: Translation of diameter for Spanish Speakers

Britannica English: Translation of diameter for Arabic Speakers

Comments on diameter

What made you want to look up diameter? Please tell us where you read or heard it (including the quote, if possible).


to take the place or position of

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