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

Keep scrolling for more

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.
See More
Recent Examples on the Web Opened in 1989 on the former site of Pepperdine University, Price’s South Vermont Avenue church was topped by a massive aluminum sphere known as the FaithDome, 320 feet in diameter and 63 feet high. Los Angeles Times, "Rev. Frederick K.C. Price of Crenshaw Christian Center in South L.A. dies from COVID-19," 14 Feb. 2021 It’s 21 feet tall, 75 feet in diameter, and can surround 270 degrees of a set (including the ceiling). Brent Rose, Wired, "The Hollywood Tech Tricks Getting Film Crews Back on Set," 11 Feb. 2021 The storm drain in Northwest Washington appeared to be about two feet in diameter. Washington Post, "D.C. fire department goes into storm drain to get dog, spokesman says," 7 Feb. 2021 Its home range is about one-fourth to a half-mile in diameter. Jim Gilbert, Star Tribune, "February is a generous month in the natural world," 4 Feb. 2021 Heirloom Rose flower soap (5 inches in diameter), $42. Kara Nelson | Contributing Writer, NOLA.com, "In time for Valentine's, some sweet gift options for the ones you love (or for yourself)," 26 Jan. 2021 There will be 14 portlights, or round windows 12 inches in diameter on each side and above square windows. Kevin Spear, USA TODAY, "'They won't have to separate from ... family': Florida attraction to get glass-bottom boat for wheelchairs," 25 Jan. 2021 The National Weather Service cautioned of the potential for hail up to 2 inches in diameter, damaging winds between 60 and 80 mph and heavy rain. Dallas News, "Storms could bring hail, damaging winds to Dallas-Fort Worth late Sunday," 24 Jan. 2021 For comparison, a human hair is about 70 micrometers in diameter. Byron Erath, The Conversation, "How to stay safe with a fast-spreading new coronavirus variant on the loose," 19 Jan. 2021

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.

See More

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

Keep scrolling for more

Learn More about diameter

Time Traveler for diameter

Time Traveler

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

See more words from the same century

Statistics for diameter

Last Updated

20 Feb 2021

Cite this Entry

“Diameter.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/diameter. Accessed 2 Mar. 2021.

Style: MLA
MLA Chicago APA Merriam-Webster

Keep scrolling for more

More Definitions for diameter



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

Keep scrolling for more

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).


Test Your Vocabulary

February 2021 Words of the Day Quiz

  • squirrel in winter
  • Which is a synonym of perdure?
True or False

Test your knowledge - and maybe learn something along the way.

Universal Daily Crossword

A daily challenge for crossword fanatics.

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!