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

diametral

dī-ˈa-mə-trəl 

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

Maybe, but one that measures 45mm in diameter when most brands are slimming and trimming millimeters off the size of the cases? —Roberta Naas, Forbes, 18 Oct. 2024

Photo : Blake Buettner A. Lange & Söhne Saxonia Thin The Saxonia thin proves that A. Lange & Söhne can do formalwear as well as anyone, with a graceful yellow gold case that measures 37mm in diameter, and a mere 5.9mm in thickness. —Blake Buettner, Robb Report, 15 Oct. 2024

Fully stacked on the Super Heavy booster, Starship stands 397 feet tall and is about 30 feet in diameter. —Michael Sheetz, NBC News, 13 Oct. 2024

According to Sany, it's also set a record for the largest onshore turbine rotor diameter at 886 ft (270 m), surpassing the previous largest onshore wind turbine on the planet, Goldwind's 12-MW design launched in 2023 with a 787-ft (240-m) rotor diameter. —Abhimanyu Ghoshal, New Atlas, 11 Oct. 2024

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

Kids 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