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.

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diameter British  

/ daɪˈæmɪtə /

noun

1. 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

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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.

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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.

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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

Handling both the charge and recharge cycles is a reactor about 15 inches in diameter and 8 feet tall that can generate around 100 kilowatts of heat.

From The Wall Street Journal • Mar. 27, 2026

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

From Barron's • Mar. 7, 2026

"At the same time, changing and adjusting the diameter of the microdroplets containing a biologically active substance nanodose is only possible by varying the oil phase flow rate."

From Science Daily • Jan. 17, 2026

Measuring roughly 55 feet long and 18 feet wide, the float featured a dense seascape of corals, fish and oversize sea stars, some spanning 4 feet in diameter.

From Los Angeles Times • Jan. 3, 2026

At the base, it may have been a couple of miles in diameter.

From "Gregor the Overlander" by Suzanne Collins

Related Words

• width