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
With the initial supercell thunderstorms in northeast Kansas, southeast Nebraska, and northwest Missouri, there is a potential for hail that is greater than 2 inches in diameter, damaging winds of 70 to 80 mph, and heavy rains.
—
Kansas City Star, 18 May 2026
The blooms measure six to eight inches in diameter.
—Mary Marlowe Leverette, The Spruce, 18 May 2026
Based on assumptions about how much light is reflected, 2026JH2 is currently estimated to be between 15 and 30 meters (50 and 100 feet) in diameter.
—Jacopo Prisco, CNN Money, 18 May 2026
Severe weather could include winds up to almost 75 mph and hail less than 2 inches in diameter.
—Daniel McFadin, Arkansas Online, 17 May 2026
See All Example Sentences for diameter
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Kansas City Star, 18 May 2026
The blooms measure six to eight inches in diameter.
—Mary Marlowe Leverette, The Spruce, 18 May 2026
Based on assumptions about how much light is reflected, 2026JH2 is currently estimated to be between 15 and 30 meters (50 and 100 feet) in diameter.
—Jacopo Prisco, CNN Money, 18 May 2026
Severe weather could include winds up to almost 75 mph and hail less than 2 inches in diameter.
—Daniel McFadin, Arkansas Online, 17 May 2026
See All Example Sentences for diameter
Cite this Entry
“Diameter.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/diameter. Accessed 20 May. 2026.
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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