perimeter

American  

[puh-rim-i-ter] / pəˈrɪm ɪ tər /

noun

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

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

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

The bet rested on a single Météo-France weather sensor sitting near the perimeter of Charles de Gaulle Airport on a publicly accessible road.

From The Wall Street Journal • May 5, 2026

He was able to get into the hotel because the hotel was open to the public: the actual security perimeter was narrower.

From Slate • Apr. 26, 2026

Commenting on how security might change, some experts said they expected some stronger measures for Trump events now, such as a wider perimeter.

From BBC • Apr. 26, 2026

The banks that lend to private credit funds are within the perimeter, and their exposure has grown by an order of magnitude over the past 10 years.

From MarketWatch • Apr. 22, 2026

Ben was becoming aware of the voices of satellite greasers moving in and around the perimeter of the fight.

From "The Great Santini" by Pat Conroy

Related Words

• boundary
• confines
• edge
• fringe
• periphery