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

To put the size of these particles in perspective, the average human hair is roughly 70 micrometers in diameter, which is about 30 times larger than the largest fine particles of particulate matter. —Hayleigh Evans, The Arizona Republic, 16 Dec. 2024

Rising above 45 meters and crowned by a giant star of 17 meters in diameter, this walk-through tree offers light shows and music every hour from 6:30 p.m. to 9:30 p.m. and is accompanied by eight other trees of lights instead of hanging decoration. —Cecilia Rodriguez, Forbes, 16 Dec. 2024

Before transferring the baking sheet to the oven, use a clean hand or the bottom of a glass to press the dough balls into rounds that are ½ inch thick and 4 inches in diameter. —Karla Walsh, Better Homes & Gardens, 16 Dec. 2024

Mysterious drones start appearing in east Nov 18: Witness accounts begin spotting several large drones in New Jersey measuring around 6 feet in diameter at night usually between dusk to 11 p.m, according to the Asbury Park Press, part of the USA TODAY Network. —Anthony Robledo, USA TODAY, 14 Dec. 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