perimeter

American  

[puh-rim-i-ter] / pəˈrɪm ɪ tər /

noun

• perimeters
  plural

1. a line bounding or marking off an area.

   The police created a perimeter with caution tape around the crime scene.

2. the outermost limits.

   Under the new regulations, the smoke-free area for playgrounds and sports areas extends 20 meters from the perimeter of each site.

3. Geometry.

   1. the border or outer boundary of a two-dimensional figure.

   2. the length of such a boundary.

4. Military. a fortified boundary that protects a troop position.

5. Ophthalmology. an instrument for determining the peripheral field of vision.

6. Basketball. Often the perimeter

   1. Also called three-point line. a semicircular line on a basketball court surrounding the basket, outside of which field goals are worth three points rather than two.

   2. the area outside this line (often used attributively).

      There's no player in the NBA who puts more pressure on opposing defenses from the perimeter than him.

      The team needs an efficient point guard with a great perimeter shot.

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perimeter British  

/ pəˈrɪmɪtə /

noun

1. maths

   1. the curve or line enclosing a plane area

   2. the length of this curve or line

2. 1. any boundary around something, such as a field

   2. ( as modifier )

      a perimeter fence

      a perimeter patrol

3. a medical instrument for measuring the limits of the field of vision

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perimeter Scientific  

/ pə-rĭm′ĭ-tər /

1. The sum of the lengths of the segments that form the sides of a polygon.

2. The total length of any closed curve, such as the circumference of a circle.

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Other Word Forms

Derived Forms

• perimetry
  noun
• perimeterless
  adjective
• perimetral
  adjective
• perimetric
  adjective
• perimetrical
  adjective
• perimetrically
  adverb

Inflected Forms

Nouns

• perimeters
  plural

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Etymology

Origin of perimeter

First recorded in 1585–95; from French périmètre, from Latin perimetros (feminine), from Greek perímetron (neuter); equivalent to peri- + -meter

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Explanation

The noun perimeter refers to the border of an enclosed space. The perimeter of a house is its property line. For a country, it would be that country’s borders. From Latin peri meaning “around” and metron meaning “measure,” a perimeter is basically a boundary of any kind, measuring around the shape. In mathematics, perimeter refers to the length of this boundary. In geometry class, you might be asked to calculate the perimeter of a polygon, which is the sum of the length of each side. You might also hear this word used by members of the military or a police force as in “secure the perimeter” or “the perimeter has been breached.” A basketball player that likes to shoot from the three point line is said to “operate on the perimeter.”

Example Sentences

See Examples For:

perimeter perimeters

AwareCA pulls evacuation updates and fire perimeter maps from official sources in near-real time and allows local fire and police departments to post updates directly.

From Los Angeles Times ● Oct. 30, 2026

Outside the perimeter fence, daily life bears little resemblance to the military activity unfolding inside.

From Barron's ● Oct. 27, 2026

A non-combustible perimeter using materials like gravel, free of plants, wooden decks and furniture, to stop windblown ember ignitions.

From The Wall Street Journal ● Oct. 21, 2026

Tees Valley Wildlife Trust said flooding and damage to the colony's perimeter fence contributed to difficult conditions for the birds.

From BBC ● Oct. 15, 2026

He scanned the fountain without showing much real interest before strolling around the perimeter.

From "Glitch" by Laura Martin

Thursday’s action ramps up the pressure on the institutions, which were sent a document by the financial protection agency demanding data about their loans in Eaton and Palisades fire perimeters.

From Los Angeles Times ● Oct. 15, 2026

He appeared to suggest progress towards an agreement had been made, saying that the "perimeters of a deal has been agreed to".

From BBC ● Aug. 2, 2026

Police may close roads, establish perimeters, kettle crowds, redirect traffic, block movement, and call those acts public order.

From Slate ● Jul. 27, 2026

It would require combat troops to secure perimeters, engineers with excavating equipment to search through debris and check for mines and booby traps, and special-operations forces with expertise in handling nuclear material.

From The Wall Street Journal ● Mar. 27, 2026

“We would go around to these villages and set up perimeters of defense,” Horan explained.

From "Boots on the Ground: America's War in Vietnam" by Elizabeth Partridge

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Related Words

• boundary
• confines
• edge
• fringe
• periphery

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