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
Its coma is about 130,000 miles (209,000 kilometers) in diameter, and its tail extends around 18 million miles (29 million kilometers) into space.
—
Jamie Carter, Forbes, 31 Oct. 2024
The eclipse lasted about 30 seconds, which makes the minutes-long solar eclipses seen from Earth seem epic — but the events are comparatively brief on Mars because Phobos is about 157 times smaller in diameter than Earth’s moon, according to NASA.
—Ashley Strickland, CNN, 31 Oct. 2024
Miranda is the smallest of Uranus' large moons—after Titania, Oberon, Umbriel and Ariel—at about 290 miles in diameter, about one-seventh the size of our moon.
—Nina Turner, Newsweek, 31 Oct. 2024
Seven feet tall and 12 feet in diameter, Blue Ghost is flying cargo under NASA’s Commercial Lunar Payload Services program.
—Michael Sheetz, CNBC, 29 Oct. 2024
See all Example Sentences for diameter 
Jamie Carter, Forbes, 31 Oct. 2024
The eclipse lasted about 30 seconds, which makes the minutes-long solar eclipses seen from Earth seem epic — but the events are comparatively brief on Mars because Phobos is about 157 times smaller in diameter than Earth’s moon, according to NASA.
—Ashley Strickland, CNN, 31 Oct. 2024
Miranda is the smallest of Uranus' large moons—after Titania, Oberon, Umbriel and Ariel—at about 290 miles in diameter, about one-seventh the size of our moon.
—Nina Turner, Newsweek, 31 Oct. 2024
Seven feet tall and 12 feet in diameter, Blue Ghost is flying cargo under NASA’s Commercial Lunar Payload Services program.
—Michael Sheetz, CNBC, 29 Oct. 2024
See all Example Sentences for diameter
These examples are programmatically compiled from various online sources to illustrate current usage of the word 'diameter.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.
Dictionary Entries Near diameter
Cite this Entry
“Diameter.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/diameter. Accessed 5 Nov. 2024.
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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