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  

/ ˌpɛrɪˈmɛtrɪk, 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

Etymology

Origin of perimeter

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

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

Seven aircraft from Germany, Norway, Belgium and Sweden were carrying out water drops in and around the burned perimeter where ground temperatures remained "extremely high".

From Barron's ● Aug. 20, 2026

The fire service has said the perimeter of the blaze has been brought under control.

From BBC ● Aug. 14, 2026

Authorities said on Wednesday that better overnight weather conditions had helped crews reduce the intensity of the fires and stabilise their perimeter.

From Barron's ● Jul. 29, 2026

That’s invaluable when you’re going with Doncic and Austin Reaves on the perimeter.

From Los Angeles Times ● Jul. 28, 2026

Although the stampede continues unabated, at least I know Marlena won’t be trampled before I can navigate the perimeter of the tent.

From "Water for Elephants" by Sara Gruen

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

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

The latrines that ringed the encampment were overflowing and swarming with flies, and she saw faint greenish fuzz on many of the sharpened stakes that protected the perimeters.

From "A Clash of Kings" by George R.R. Martin

Related Words

• boundary
• confines
• edge
• fringe
• periphery