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

Astronomers estimate that several hundred thousand more KBOs measuring over 10 miles (16 kilometers) in diameter could lurk in this icy donut, which begins around 2.8 billion miles (4.5 billion km) from the sun. —Robert Lea, Space.com, 5 Mar. 2025

The space rock could be anywhere between around 33 and 72 feet in diameter, noted the JPL's Center for Near-Earth Object Studies (CNEOS). —Thomas G. Moukawsher, Newsweek, 4 Mar. 2025

Almost all colors are available and blossom size may range from very tiny to several inches in diameter. —Dawn Pettinelli, Hartford Courant, 1 Mar. 2025

The only problem was, the robots were a bit above 5 centimeters in diameter. —Ars Technica, 1 Mar. 2025

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

Rhymes for diameter

• parameter
• pentameter

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