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

"Targeting or reaching the perimeter of a nuclear facility in the Gulf crosses a psychological and strategic threshold," said Karim Bitar, a lecturer at Sciences Po in Paris.

From Barron's • May 18, 2026

While two were intercepted, the third drone struck an electrical generator "outside the inner perimeter" of the Barakah Nuclear Power Plant in Abu Dhabi, sparking a fire.

From BBC • May 17, 2026

Hig’s days are spent flying perimeter patrols, scanning for signs of life — or trouble — until he encounters Margaret Qualley’s Cima, a medic guarding her own small foothold in the ruined world.

From Los Angeles Times • May 14, 2026

For all the romance of walking Manhattan’s perimeter, most of it traces highways, with views of the Bronx and Queens.

From The Wall Street Journal • May 14, 2026

I was about to become part of a country that was much more rich and interesting because it had no walls built around its perimeter.

From "Americanized" by Sara Saedi

Related Words

• boundary
• confines
• edge
• fringe
• periphery