noun di·am·e·ter \dī-ˈa-mə-tər\

: 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

Full Definition of DIAMETER

:  a chord passing through the center of a figure or body
:  the length of a straight line through the center of an object
:  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>
di·am·e·tral \-ˈa-mə-trəl\ adjective

Examples of DIAMETER

  1. The dotted line indicates the diameter of the circle.
  2. What is the diameter of the tree trunk?
  3. Dig a hole that's two feet deep and three feet in diameter.

Origin of DIAMETER

Middle English diametre, from Middle French, from Latin diametros, from Greek, from dia- + metron measure — more at measure
First Known Use: 14th century

Other Mathematics and Statistics Terms

abscissa, denominator, divisor, equilateral, exponent, hypotenuse, logarithm, oblique, radii, rhomb
DIAMETER Defined for Kids


noun di·am·e·ter \dī-ˈa-mə-tər\

Definition of DIAMETER for Kids

:  a straight line that runs from one side of a figure and passes through the center <Measure the diameter of the circle.>
:  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


noun di·am·e·ter \dī-ˈam-ət-ər\

Medical Definition of DIAMETER

:  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>
:  one of the maximal breadths of a part of the body <the transverse diameter of the inlet of the pelvis>
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