diameter

noun di·am·e·ter \ dī-ˈa-mə-tər \

Updated on: 16 Apr 2018

Definition of diameter

1 mathematics : a chord (see ³chord 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

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diametral

play \-ˈa-mə-trəl\ adjective

See diameter defined for English-language learners

See diameter defined for kids

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 of diameter from the Web

CT Kruger/Now News Group Cooking maple syrup all starts with a hole 7/16ths of an inch in diameter being drilled into a maple tree.

— tyler langan, Milwaukee Journal Sentinel, "Lavern Schmitz makes maple syrup the old-fashioned way," 11 Apr. 2018
Improvise: Don’t have a small circle cookie cutter (about 1½ inches in diameter)?

— robin miller, azcentral, "Have a date with Netflix? Easy, healthy finger food recipes to get you through binge-worthy shows," 11 Apr. 2018
Measuring about 2 1/2 feet in diameter, it's recognized as the one and only public memorial of the life and career of Louisiana Gov. Richard Leche, whose administration was famously undone by rampant corruption in 1939.

— mike scott, NOLA.com, "In a Mandeville swamp, an accidental memorial to a historically crooked politican," 10 Apr. 2018
Model-specific wheels up to 22 inches in diameter will be available.

— jeff yip, Houston Chronicle, "GMC hatches next-gen 2019 half-ton, offers off-road version, carbon-fiber bed," 7 Apr. 2018
These particles, which are less than 2.5 micrometres (thousandths of a millimetre) in diameter, are blamed for various respiratory diseases and lung cancer.

— The Economist, "Wood-burning stoves are in fashion but cause serious pollution," 5 Apr. 2018
The long-necked dinosaur footprints were each about the size of a trash can lid, Ms. dePolo said, with the largest being more than two feet in diameter.

— nicholas st. fleur, New York Times, "In Footprints on Scotland’s Isle of Skye, Signs of a Dinosaur Playground," 4 Apr. 2018
Jesse said He then moved through a pipe that was just four feet in diameter and was stuck there for more than 12 hours before rescuers found him.

— jennifer calfas, Time, "'I Was Just Praying to God to Help Me.' 13-Year-Old Boy Trapped in a Sewer Pipe for 12 Hours Describes His Harrowing Ordeal," 3 Apr. 2018
And, according to the Guinness World Records, the world’s largest chicken egg, which was nine inches in diameter and had five yolks.

— mari uyehara, Bon Appetit, "Why Do Some Eggs Have Double Yolks? An Investigation.," 27 Mar. 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'diameter.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

Origin and Etymology of diameter

Middle English diametre, from Middle French, from Latin diametros, from Greek, from dia- + metron measure — more at measure

NEW! Time Traveler

First Known Use: 14th century

in the meaning defined at sense 1

See Words from the same year

Other Mathematics and Statistics Terms

abscissa, denominator, divisor, equilateral, exponent, hypotenuse, logarithm, oblique, radii, rhomb

DIAMETER Defined for English Language Learners

diameter

noun

Definition of diameter for English Language Learners

: a straight line from one side of something (such as a circle) to the other side that passes through the center point
: the distance through the center of something from one side to the other

DIAMETER Defined for Kids

diameter

noun di·am·e·ter \ dī-ˈa-mə-tər \

Definition of diameter for Students

1 : a straight line that runs from one side of a figure and passes through the center

Measure the diameter of the circle.

2 : the distance through the center of an object from one side to the other : thickness

the diameter of a tree trunk

Word Root of diameter

The Greek word metron, meaning “measure,” gives us the root metr. Words from the Greek metron have something to do with measuring. A thermometer is an instrument that measures temperature. A diameter is the measurement across the center of a circle. The metric system is a system used for measuring size, weight, and volume. A perimeter is the measurement of the outside of a figure or shape.