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Definition of diameter
1 mathematics : a chord (see ^{3}chord 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
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

Once out of the museum, the thieves loaded the 1.2inch thick, 20.9inch in diameter coin into a wheelbarrow, slipped into a park using a rope and fled in a getaway car, the AP reported.

The chief estimated that the debris field was about three miles in diameter.

The telescope is a 6½foot Newtonian reflecting model with a 13inch diameter.

Shape into 8 thin patties, about 2 1/2 to 3 inches in diameter.

Many are 1 or 2 inches (2.5 or 5 centimeters) in diameter.

Asteroid 1997 XF11, as it was later called, was a big one — a mile in diameter.

So scientists have been experimenting with carbon nanotubes, rolledup sheets of carbon atoms just 1 nanometer, or a billionth of a meter, in diameter.

The smoke firework is a cardboard tube that is about 1 inch in diameter and 5 inches long.
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 MerriamWebster 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
Other Mathematics and Statistics Terms
DIAMETER Defined for English Language Learners
diameter
playDefinition 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
playDefinition 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.
Medical Dictionary
diameter
playMedical Definition of diameter
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
Learn More about diameter

See words that rhyme with diameter Spanish Central: Translation of diameter Nglish: Translation of diameter for Spanish speakers Britannica English: Translation of diameter for Arabic speakers
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