diameter

noun di·am·e·ter \ dī-ˈa-mə-tər \

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

The 102-inch diameter concrete sewer line dates to 1948 and the Metropolitan Sewer District blames the failure on age.

— james bruggers, The Courier-Journal, "Sewer line sinkhole swallows portion of E. Main Street, potentially closing it for weeks," 30 Aug. 2017
But in response to public outcry, Duke scaled back its original proposal last September, from a 30-inch in diameter pipeline operating at pressures up to 600 pounds per square inch to a 20-inch pipeline running no more than 400 psi.

— carrie blackmore smith, Cincinnati.com, "Duke pipeline plan delayed over environmental concerns," 24 Aug. 2017
There are boulders that could be anywhere from 12 inches to 3 feet in diameter and could weigh up to 1,000 pounds.

— karen ridder, kansascity, "A rainbow of landscaping rock emerges from old Missouri riverbed," 19 Aug. 2017
Nursery industry standards call for the root ball to be 10 to 12 times the diameter of the trunk.

— beth botts, chicagotribune.com, "5 steps to help a new, large tree thrive," 4 Aug. 2017
That hurt quality and led to a high rejection rate by retailers because the carrots did not meet standards for color, texture, and diameter.

— harold brubaker, Philly.com, "Campbell's Bolthouse carrots have turned corner, exec says," 19 July 2017
The one whose diameter is marked as a or the one marked as b?

— philip bump, Washington Post, "Goodnight, Too-Large-to-Be-Astronomically-Accurate Moon," 18 July 2017
Large Stainless Steel #Lemon Squeezer Lemon Juicer Press for Orange Lime and Lemons Citrus 2.4’’ inner diameter, 0.88lbs Designed for effective extraction, this#hand-heldlemonsqueezer won't waste an ounce of juice.

— carly breit, Country Living, "You've Been Using a Lemon Juicer All Wrong," 14 July 2017
Once out of the museum, the thieves loaded the 1.2-inch thick, 20.9-inch in diameter coin into a wheelbarrow, slipped into a park using a rope and fled in a getaway car, the AP reported.

— alex horton, chicagotribune.com, "German police are searching for a stolen gold coin. It's the size of a manhole cover and worth $3.9 million.," 12 July 2017

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

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.