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
Prices vary from region to region, but even a relatively small stump, only 18 inches in diameter, can cost hundreds of dollars to remove professionally.
—
Daniel Scott, Better Homes & Gardens, 9 Apr. 2025
The organoids contained nearly four million cells but were slightly less than one-tenth of an inch or 2.54 mm in diameter.
—New Atlas, 9 Apr. 2025
The thin discs measured just over 5 inches in diameter with a hole in the middle.
—Aspen Pflughoeft, Miami Herald, 8 Apr. 2025
Of note, the asteroid, approximately 60 meters in diameter — roughly the width of a football field — still has a 2% chance of striking the moon.
—Sharmila Kuthunur, Space.com, 8 Apr. 2025
See All Example Sentences for diameter
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Daniel Scott, Better Homes & Gardens, 9 Apr. 2025
The organoids contained nearly four million cells but were slightly less than one-tenth of an inch or 2.54 mm in diameter.
—New Atlas, 9 Apr. 2025
The thin discs measured just over 5 inches in diameter with a hole in the middle.
—Aspen Pflughoeft, Miami Herald, 8 Apr. 2025
Of note, the asteroid, approximately 60 meters in diameter — roughly the width of a football field — still has a 2% chance of striking the moon.
—Sharmila Kuthunur, Space.com, 8 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 15 Apr. 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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