noun pe·rim·e·ter \pə-ˈri-mə-tər\

Definition of perimeter

  1. 1a :  the boundary of a closed plane figureb :  the length of a perimeter

  2. 2 :  a line or strip bounding or protecting an area

  3. 3 :  outer limits —often used in plural

  4. 4 :  the part of a basketball court outside the three-point line

Examples of perimeter in a sentence

  1. He scored from the perimeter.

  2. <soldiers guarding the perimeter of the camp>

parameter vs. perimeter

It's very easy to confuse parameter with perimeter. Not only do the two words sound the same, they both connote a boundary or limit.

When parameter is used to mean "a boundary or limit," it is usually in its plural form, and often as the object of a preposition such as within or beyond:

Let's face it, managing weight loss or maintenance can be trying enough within the parameters of a daily routine.
Geoff Kerr, Weight Watchers, November 1991

Though candor sometimes encourages Bruno to "stray beyond the parameters of good taste," his interaction with Lydia is always convincingly portrayed as a loving, tender relationship.
Ron Charles, The Washington Post, 8 Feb. 2011

In geometry, perimeter refers to the boundary of a closed plane figure. You might remember calculating perimeters in school. If each side of an equilateral triangle measures 9 feet, then the perimeter of the triangle measures 27 feet. In more general use, perimeter describes an outer stretch, as in "The college president lived in a house on the perimeter of the campus."

Parameter originally had a meaning pertaining to mathematics as well. The dictionary defines it as "an arbitrary constant whose value characterizes a member of a system (as a family of curves); also : a quantity (as a mean or variance) that describes a statistical population" as well as "an independent variable used to express the coordinates of a variable point and functions of them."

Some twentieth-century usage commentators objected to the use of a scientific-sounding word like parameter in general contexts (as in the examples above), especially to mean "a limit or boundary," theorizing that perimeter must have been what the speaker or writer intended.

However, perimeter was not often used in the phrasings that parameter is used in (that is, as the object of within or beyond) until much later. In fact, a word such as bounds or range or confines often serves as a more appropriate equivalent for parameter than the marginal connotations of perimeter:

But a true novel is an extended piece of fiction: Length is clearly one of its parameters.
Anthony Burgess, The New York Times Book Review, 5 Feb. 1984

Shields will then subsume that request in the overall City operating budget that he will recommend to the City Council in mid-March, and the Council will make its final decisions on the parameters of the budget, including any tax increases or cuts, by the end of April.
Nicholas F. Benton, The Falls Church News Press, 6 Jan. 2016

Did You Know?

The perimeter of a prison is ringed with high walls and watchtowers, and the entire perimeter of Australia is bounded by water. In geometry, you may be asked to calculate the perimeter of various geometrical shapes. In basketball, the perimeter is the area beyond the free-throw circle; a "perimeter player" tends to stay outside that circle. Try not to confuse this word with parameter, which usually means a rule or limit that controls what something is or how it can be done.

Origin and Etymology of perimeter

Middle English perimetre, from Latin perimetros, from Greek, from peri- + metron measure — more at measure

First Known Use: 15th century

Other Mathematics and Statistics Terms

PERIMETER Defined for English Language Learners


noun pe·rim·e·ter \pə-ˈri-mə-tər\

Definition of perimeter for English Language Learners

  • : the outside edge of an area or surface

  • : the total length of the lines that form a shape

  • the perimeter basketball : the area on a basketball court that is not close to the basket

PERIMETER Defined for Kids


noun pe·rim·e·ter \pə-ˈri-mə-tər\

Definition of perimeter for Students

  1. 1 :  the whole outer boundary of a figure or area

  2. 2 :  the length of the boundary of a figure

Word Root of perimeter

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 pe·rim·e·ter \pə-ˈrim-ət-ər\

Medical Definition of perimeter

  1. 1a:  the boundary of a closed plane figureb:  the length of a perimeter

  2. 2:  an instrument for examining the discriminative powers of different parts of the retina often consisting of an adjustable semicircular arm with a fixation point for the eye and variable stations for the visual stimuli

Seen and Heard

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gray or white with or as if with age

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