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
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
Good for a cool, shady location, the blooms are pale blue with purple shading nodding bells, 2.5 to 3 inches in diameter, and grows up to 15 feet tall.
—
Mary Marlowe Leverette, Southern Living, 3 May 2025
But Langbroek and others believe the landing capsule itself — a spherical object about 3 feet (1 meter) in diameter — has been circling the world in a highly elliptical orbit for the past 53 years, gradually dropping in altitude.
—Marcia Dunn, The Orlando Sentinel, 1 May 2025
At the Cretaceous-Paleogene transition 66 million years ago, an asteroid about 10 kilometers in diameter struck a shallow sea in what is today Southeast Mexico.
—David Bressan, Forbes.com, 29 Apr. 2025
While sizes may vary from set to set, an official net is 3 feet in diameter and sits 8 inches above the ground.
—Bestreviews, Mercury News, 29 Apr. 2025
See All Example Sentences for diameter
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Mary Marlowe Leverette, Southern Living, 3 May 2025
But Langbroek and others believe the landing capsule itself — a spherical object about 3 feet (1 meter) in diameter — has been circling the world in a highly elliptical orbit for the past 53 years, gradually dropping in altitude.
—Marcia Dunn, The Orlando Sentinel, 1 May 2025
At the Cretaceous-Paleogene transition 66 million years ago, an asteroid about 10 kilometers in diameter struck a shallow sea in what is today Southeast Mexico.
—David Bressan, Forbes.com, 29 Apr. 2025
While sizes may vary from set to set, an official net is 3 feet in diameter and sits 8 inches above the ground.
—Bestreviews, Mercury News, 29 Apr. 2025
See All Example Sentences for diameter
Cite this Entry
“Diameter.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/diameter. Accessed 9 May. 2025.
Copy CitationKids 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
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