pe·​rim·​e·​ter | \pə-ˈri-mə-tər \

Definition of perimeter 

1a : the boundary of a closed plane figure

b : the length of a perimeter

2 : a line or strip bounding or protecting an area

3 : outer limits often used in plural

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

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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.

Examples of perimeter in a Sentence

He scored from the perimeter. soldiers guarding the perimeter of the camp

Recent Examples on the Web

Credit Alysha Clark for Seattle’s defensive dominance on the perimeter. Percy Allen, The Seattle Times, "Three thoughts on the WNBA Finals as the series shifts to D.C.," 11 Sep. 2018 The Celtics play max-effort defense, share-the-ball on offense and can field modern lineups, going with a small rotation or big rotation depending on the circumstance with an abundance of athletic perimeter players. Jeff Zillgitt, USA TODAY, "LeBron James' exit leaves Celtics, 76ers as favorites in wide-open Eastern Conference," 2 July 2018 Garrett will be part of a deep group of perimeter players for KU this season. Gary Bedore, kansascity, "KU sophomore Garrett changes shooting form: 'I feel comfortable now'," 2 July 2018 Cons: Quickley would be the best 3-point shooter in this lineup as well, leading to some of the same concerns about floor spacing and opponents sagging off multiple perimeter players. Jon Hale, The Courier-Journal, "Who should start for Kentucky? A look at four possible 2018-19 lineups," 25 June 2018 Ayton often was covering perimeter players and handling pick-and-roll switches, making Miller believe that defense might actually prove to be his strength. Paul Coro,, "Potential No. 1 draft pick Deandre Ayton says he and Devin Booker could be "Shaq and Kobe 2.0" for Phoenix Suns," 18 June 2018 His scoring talents will add to the strong returning perimeter players: do-everything guard Kamar Baldwin, defensive stopper and heady passer Aaron Thompson, and sharpshooters Paul Jorgensen and Sean McDermott. Ben Steele, Milwaukee Journal Sentinel, "Big East men's basketball off-season stock watch: Marquette up, Villanova down," 8 June 2018 That’s especially troubling against a team like Houston, which lives on the perimeter and forces the other team’s backcourt into tiring one-on-one defense. Al Saracevic,, "After four long years of winning, are the Warriors tired?," 23 May 2018 When the Rockets switched perimeter players onto Towns, or called on their small lineup with P.J. Tucker on him, Towns went to work inside, scoring 13 points with some of his most determined play of the series. Jonathan Feigen, Houston Chronicle, "Rockets roll past Timberwolves to finish off first-round series with rout," 25 Apr. 2018

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

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First Known Use of perimeter

15th century, in the meaning defined at sense 1a

History and Etymology for perimeter

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

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Statistics for perimeter

Last Updated

14 Nov 2018

Look-up Popularity

Time Traveler for perimeter

The first known use of perimeter was in the 15th century

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More Definitions for perimeter



English Language Learners Definition of perimeter

: 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


pe·​rim·​e·​ter | \pə-ˈri-mə-tər \

Kids Definition of perimeter

1 : the whole outer boundary of a figure or area

2 : the length of the boundary of a figure


pe·​rim·​e·​ter | \pə-ˈrim-ət-ər \

Medical Definition of perimeter 

1a : the boundary of a closed plane figure

b : the length of a perimeter

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

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Comments on perimeter

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to clear from alleged fault or guilt

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