diameter

noun

di·​am·​e·​ter dī-ˈa-mə-tər How to pronounce diameter (audio)
Synonyms of diameternext
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 How to pronounce diameter (audio)
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
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
Key features: 10x magnification, 25mm objective lens diameter, non-removable glass solar filters, 5.7-degree angular field of view, 11.5 oz weight. — Paul Brett, Space.com, 17 Mar. 2025 At the scene, crews noticed that a tree measuring about 3 feet in diameter had fallen through the middle of a family’s residential trailer. — Simone Jasper, Charlotte Observer, 17 Mar. 2025 The steel case is 39.5mm in diameter with a lug-to-lug of 46mm, and thickness varies from 8.1mm to 9.8mm due to its curved profile. — Bhanu Chopra, Forbes, 17 Mar. 2025 Pi is the ratio of the circumference to the diameter of a circle: π = C/d. — Rhett Allain, WIRED, 14 Mar. 2025 See All Example Sentences for diameter

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

Time Traveler
The first known use of diameter was in the 14th century

Rhymes for diameter

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Browse Nearby Words

diameter
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Cite this Entry

“Diameter.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/diameter. Accessed 25 Mar. 2025.

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Kids Definition

diameter

noun
di·​am·​e·​ter dī-ˈam-ət-ər How to pronounce diameter (audio)
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 How to pronounce diameter (audio)
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

More from Merriam-Webster on diameter

Thesaurus: All synonyms and antonyms for diameter

Nglish: Translation of diameter for Spanish Speakers

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