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

Its coma is about 130,000 miles (209,000 kilometers) in diameter, and its tail extends around 18 million miles (29 million kilometers) into space. —Jamie Carter, Forbes, 31 Oct. 2024

The eclipse lasted about 30 seconds, which makes the minutes-long solar eclipses seen from Earth seem epic — but the events are comparatively brief on Mars because Phobos is about 157 times smaller in diameter than Earth’s moon, according to NASA. —Ashley Strickland, CNN, 31 Oct. 2024

Miranda is the smallest of Uranus' large moons—after Titania, Oberon, Umbriel and Ariel—at about 290 miles in diameter, about one-seventh the size of our moon. —Nina Turner, Newsweek, 31 Oct. 2024

Seven feet tall and 12 feet in diameter, Blue Ghost is flying cargo under NASA’s Commercial Lunar Payload Services program. —Michael Sheetz, CNBC, 29 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