di·am·e·ter | \dī-ˈa-mə-tər \

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 \-ˈa-mə-trəl \ 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

In Melbourne, Australia, 4% of the sun’s diameter will be covered, which means only a sliver of sun will be darkened by the eclipse. Gabby Raymond, Time, "A Partial Solar Eclipse Is Coming on Friday the 13th. That Hasn't Happened in 40 Years," 10 July 2018 Campfires with a diameter of less than 3 feet are allowed but not advised, according to the Alaska Division of Forestry, which suspended burning in the Mat-Su. Devin Kelly, Anchorage Daily News, "Dry weather keeps burn bans in effect for Anchorage and Mat-Su," 6 July 2018 The lunar far side is in a constant state of radio blackout because radio transmissions can't penetrate the moon, which has a diameter of 2,160 miles. NBC News, "China plans historic mission to the moon's 'dark' side," 15 June 2018 With a diameter of 17 inches, the vase can also be flipped around and used as a table or a stool — an interpretation on the Danish design tradition of merging form and function. James Clasper, New York Times, "Artist to Know: the Danish Sculptor Making Objects for Noma," 13 June 2018 The shock wave would reach a diameter of nearly 3.2 miles, shattering windows as far as Gramercy Park and the American Museum of Natural History. Daily Intelligencer, "This Is What a Nuclear Bomb Looks Like," 12 June 2018 Look for a diameter of at least 8 inches, which will require less carving. Andrew Del-colle And Lara Sorokanich, Popular Mechanics, "How to Make a Bow and Arrow By Hand," 5 June 2018 Each of the wind farm’s turbines climb 262 feet in height, with blades attached to rotors that stretch to a diameter of 351 feet. Rob Nikolewski, sandiegouniontribune.com, "Tule Wind Project back up after being offline for more than 5 weeks," 1 June 2018 The existing culvert will be replaced with high-density polyethylene plastic pipe with a 24-inch diameter, meeting specifications set by the city of Houston. Melanie Feuk, Houston Chronicle, "KSA to replace collapsed culvert at flood-prone River Grove Park in Kingwood for $33K," 5 May 2018

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

14 Oct 2018

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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 \

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 \

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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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).


one that holds something together

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