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

They said they installed 26 misting stations around the perimeter of the building.

From Los Angeles Times ● Aug. 6, 2026

Sheriff’s deputies returned to the Guthrie house the next day—Wednesday, Feb. 4—and unspooled a perimeter of police tape around the house.

From The Wall Street Journal ● Aug. 2, 2026

Satellite images show that - over time - what appears to be a large perimeter fence has been built around the site, following the 12-day war between Israel and Iran in June 2025.

From BBC ● Aug. 1, 2026

Officers established a perimeter and began searching for the suspect, who was described as a man in a reflective vest.

From Los Angeles Times ● Aug. 1, 2026

All the while, Blake kept watch for weaknesses in the prison's perimeter.

From "Spies: The Secret Showdown Between America and Russia" by Marc Favreau

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

From Barron's ● Aug. 3, 2026

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

From Slate ● Jul. 27, 2026

Setting those perimeters impressed producers while also shaping her personal and creative evolution.

From Los Angeles Times ● May 13, 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