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

The pair, aged 36 and 32 and who live in the UK, were subsequently arrested inside the perimeter a few hours after searches found a small breach of the fence at the site.

From BBC ● Oct. 9, 2026

At RAF Molesworth, police said the men entered after cutting a hole in the perimeter fence, another example of how difficult it is to protect military bases.

From The Wall Street Journal ● Oct. 8, 2026

The Lakers have stocked their team with versatile perimeter defenders to help complement their offensive-minded backcourt of Doncic and Reaves.

From Los Angeles Times ● Oct. 7, 2026

Dozens of locals, some equipped with binoculars and long-lensed cameras, gathered near the air base's perimeter fence to watch the highly anticipated arrival of the jets.

From Barron's ● Oct. 2, 2026

Alfhercht and Wielaf conferred with rapid gestures, and then Alfhercht paced around the perimeter of the field, studying the ground with a thin-lipped mouth.

From Anya and the Nightingale by Sofiya Pasternack

Nearly 6,000 homeless people could be forced to move when security officials impose expansive security perimeters in advance of the 2028 Summer Olympics in Los Angeles, researchers estimated in a new study.

From Los Angeles Times ● Sep. 4, 2026

He pulled back from that threat on Saturday, saying the "perimeters" of a deal were there.

From Barron's ● Aug. 3, 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

For one thing, every day, the perimeters of her former estate seemed to double, as did the contents of her almari and coffer boxes.

From "Interpreter of Maladies" by Jhumpa Lahiri

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Related Words

• boundary
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