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

The small asteroid, which is more than 3 miles in diameter, approaches so close to the sun that it was named for the son of the sun-god Helios, who in Greek mythology lost control of his father's chariot and set the Earth ablaze. —Eric Lagatta, USA TODAY, 6 Dec. 2024

This is a more substantial watch than we’re used to seeing in the Nautilus range, at 43.5 mm in diameter and 12.3 mm in thickness, but this is a statement piece as much as anything, especially when rendered in rose gold. —Blake Buettner, Robb Report, 6 Dec. 2024

For example, a 2-inch diameter tree needs 20 gallons per watering applied within the dripline of the tree. —Mary Marlowe Leverette, Southern Living, 4 Dec. 2024

It was later calculated to measure about 66 feet (20 meters) in diameter. —Jamie Carter, Forbes, 4 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