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

Other Words from diameter

diametral \ dī-​ˈa-​mə-​trəl How to pronounce diameter (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.
Recent Examples on the Web Also sitting on the ground are dozens of 4-foot-diameter concrete collars and vaults that will tie each lot into the main sewer line and miles of drip irrigation tubes. Brian Maffly, The Salt Lake Tribune, 5 May 2022 This option—on sale now for under $100—has an 11-foot diameter that can cover a table and four chairs, featuring a crank handle and push-button tilt. Kylee Mcguigan, Popular Mechanics, 5 May 2022 The concert venue’s hillside was washed out after an air release valve failed during maintenance of a 54-inch diameter water line last August. Sam Whiting, San Francisco Chronicle, 2 May 2022 The force of water traveling through 15-foot diameter pipes hits and spins turbines which then generate power. René Marsh, CNN, 30 Apr. 2022 Essentially, SpinLaunch works by attaching the launch vehicle to the end of a carbon-fiber arm housed in a 300-foot diameter steel vacuum chamber. Joshua Hawkins, BGR, 12 Apr. 2022 The 11-inch-diameter lenses at the top, ground to perfection, gather light from distant planets, stars and galaxies. Dean Regas, The Enquirer, 8 Apr. 2022 Inversion aims to develop a four-foot-diameter capsule carrying a payload equivalent to the size of a few carry-on suitcases by 2025. New York Times, 7 Mar. 2022 Some martins will nest in single gourds with about a 6-inch square compartment and a 2-inch-diameter entrance hole, but most end up selecting an apartment of that approximate size in a complex of 12 to 24 compartments. Calvin Finch, San Antonio Express-News, 4 Mar. 2022 See More

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.

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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Dictionary Entries Near diameter



diameter tape

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Statistics for diameter

Last Updated

15 May 2022

Cite this Entry

“Diameter.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/diameter. Accessed 17 May. 2022.

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More Definitions for diameter


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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