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Synonyms

diameter

American  
[dahy-am-i-ter] / daɪˈæm ɪ tər /

noun

  1. Geometry.

    1. a straight line passing through the center of a circle or sphere and meeting the circumference or surface at each end.

    2. a straight line passing from side to side of any figure or body, through its center.

  2. the length of such a line.

  3. the width of a circular or cylindrical object.

diameter British  
/ daɪˈæmɪtə /

noun

    1. a straight line connecting the centre of a geometric figure, esp a circle or sphere, with two points on the perimeter or surface

    2. the length of such a line

  2. the thickness of something, esp with circular cross section

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
diameter Scientific  
/ dī-ăm′ĭ-tər /

  1. A straight line segment that passes through the center of a circle or sphere from one side to the other.

  2. The length of such a line segment.

diameter Cultural  

  1. A straight line passing through the center of a figure, especially a circle or sphere, and joining two opposite points on its circumference.

Etymology

Origin of diameter

First recorded in 1350–1400; Middle English diametre, from Old French, from Latin diametros, from Greek diámetros “diagonal, diameter,” from dia- dia- + -metros, derivative of métron meter 1

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

With a steady hand, she manoeuvred a huge wind turbine section, five metres in diameter, across the yard.

From Barron's • Mar. 7, 2026

The device measures approximately 10 cm in diameter and 30 cm long and has a red anodised finish.

From BBC • Feb. 6, 2026

By analyzing its length and diameter, the researchers assessed whether the bones could withstand the forces produced during hopping.

From Science Daily • Jan. 23, 2026

Some early models of the satellite dishes measured 16 feet in diameter, and hundreds of thousands of them sprouted up across the country.

From The Wall Street Journal • Jan. 22, 2026

He’d brought the two coils of rope from the locker and he measured the diameter of them with the span of his hand and that by three and then counted the number of coils.

From "The Road" by Cormac McCarthy

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.