diameter

noun

di·​am·​e·​ter dī-ˈa-mə-tər 

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

diametral

dī-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.

Recent Examples on the Web

The West Hollywood structure would be a great deal smaller, at 49 feet in diameter. —Karen Garcia, Los Angeles Times, 14 Nov. 2023

But the real genius feature is the interior waterproof pouch, which holds water bottles measuring up to 3.5 inches in diameter while simultaneously keeping them from becoming scratched. —Jamie Allison Sanders, Peoplemag, 13 Nov. 2023

That means a tree with a trunk three inches in diameter would need three quarts per day. —Katherine Owen, Southern Living, 12 Nov. 2023

One munition was a 75-mm projectile that was 3 inches in diameter and 11 inches long. —Marlene Lenthang, NBC News, 10 Nov. 2023

Some of debris is quite small, while other parts are boulder-like in size, roughly 100 meters in diameter, says Erica Jawin, a geologist at the Smithsonian Air and Space Museum. —Joshua Rapp Learn, Discover Magazine, 9 Nov. 2023

The new island was about 100 meters, or 328 feet, in diameter as of Oct. 30, according to a report by the Earthquake Research Institute at the University of Tokyo. —Mike Ives, New York Times, 8 Nov. 2023

The small sample at the museum—the first available to the public—is about 0.3 inches in diameter and weighs just 0.005 ounces. —Will Sullivan, Smithsonian Magazine, 7 Nov. 2023

What to Know About Napkin Rings Before Shopping Dimensions Most napkin rings have a hole around 2 inches in diameter, but this could vary based on design. —Maya Polton, Better Homes & Gardens, 2 Nov. 2023

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Word History

Etymology

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

First Known Use

14th century, in the meaning defined at sense 1

Kids Definition

diameter

noun

di·​am·​e·​ter dī-ˈam-ət-ər 

1

: a straight line passing through the center of a figure or body

especially : a line segment through the center of a circle with its ends on the circle's circumference

2

: the length of a diameter

Medical Definition

diameter

noun

di·​am·​e·​ter dī-ˈam-ət-ər 

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