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

"The fire has been contained within its perimeter and brought under control, with no danger of flames spreading," the head of the regional government of Andalusia, Juan Manuel Moreno, told reporters.

From Barron's ● Jul. 12, 2026

Two fixed-wing airplanes arrived on scene rapidly and dropped flame retardant around the perimeter of the blaze, while three helicopters dropped water from above, according to Ventura County Fire spokesperson Andrew Dowd.

From Los Angeles Times ● Jul. 10, 2026

“No trespassing” signs plaster trees on the perimeter.

From The Wall Street Journal ● Jul. 7, 2026

Later, on Idol, the band walked the perimeter of the venue, stopping to pose for photos and wave to the faithful, as dancers waved giant flags.

From BBC ● Jul. 7, 2026

Helen asks, watching me circle the perimeter of the retiring room again.

From "The Brightwood Code" by Monica Hesse

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

From Slate ● Jul. 27, 2026

Flights resume on April 16, particularly on the eastern and southern perimeters of the island.

From The Wall Street Journal ● May 23, 2026

"However, officers were required to enforce... life-saving guidelines when crowds later exceeded authorised capacity and seemingly attempted to breach security perimeters into the Old City," they said.

From Barron's ● Mar. 20, 2026

Preparations included layered security perimeters, traffic management plans, and a highly visible police presence throughout the Hollywood area.

From BBC ● Mar. 16, 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

Related Words

• boundary
• confines
• edge
• fringe
• periphery