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 This super-quiet fan has a 16-inch diameter with 5 blades and 5 speed settings, producing up to 2,436 cubic feet per minute. Tony Vaz, Popular Science, "Great fans to help you keep your cool," 31 Jan. 2020 There should be about a 5-inch diameter opening in the center. Susan Selasky, Detroit Free Press, "Guacamole, sliders, wings and more: Must have Super Bowl snacks," 26 Jan. 2020 The roundabout Residents were shown two plans for reconfiguring the roundabout at Chagrin Boulevard and Lander Road, both of which would reduce the circle’s current diameter. cleveland, "Pepper Pike residents attend Beech Brook development open house ahead of rezoning vote," 26 Jan. 2020 Extra-strong wall-mount double-sided tape Four feet of silicone fuel tubing with a 5/32-inch inner diameter. Scientific American, "Lift a Large Load Using Liquids," 23 Jan. 2020 The Siphon has a 1.75-inch cutting diameter delivered by three .035-inch blades and a stainless steel chisel tip. Tony Hansen, Outdoor Life, "7 New Broadheads for 2020," 13 Jan. 2020 But by diving into a physically and mentally grueling sport—in which one competes in a 28-inch diameter circle with an opponent until someone is pinned — girls have proven that gender is no barrier in wrestling. David J. Kim, The Courier-Journal, "Pinning doubt: All-girls wrestling teams proving gender is no barrier on the mat," 19 Dec. 2019 The inside of a 21-foot-diameter steel pipe needed recoating to protect against rust, officials say. USA TODAY, "Purple potatoes, suffragette mountain, pig your pardon?: News from around our 50 states," 17 Dec. 2019 The spacecraft will travel for more than a year to the double asteroid Didymos, a 2,560-foot diameter main body orbited by a 525-foot satellite moonlet called Didymos B or Didymoon. Jason Daley, Smithsonian, "A Spacecraft Will Follow NASA’s Asteroid-Smashing Mission to Measure the Effects of the Impact," 4 Dec. 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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Time Traveler for diameter

Time Traveler

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

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Statistics for diameter

Last Updated

18 Feb 2020

Cite this Entry

“Diameter.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/diameter. Accessed 26 Feb. 2020.

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More Definitions for diameter


How to pronounce diameter (audio)

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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