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• pi
  pi

  noun

  the 16th letter of the Greek alphabet (Π, π).
• PI
  PI

  personal injury.
• Pi.
  Pi.

  abbreviation

  piaster.
• P.I.
  P.I.

  abbreviation

  Philippine Islands.

pi

¹ American  

[pahy] / paɪ /

noun

pis plural

1. the 16th letter of the Greek alphabet (Π, π).

2. the consonant sound represented by this letter.

3. Mathematics.

   1. the letter π, used as the symbol for the ratio of the circumference of a circle to its diameter.

   2. the ratio itself: 3.141592+.

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pi ² American  

[pahy] / paɪ /

Or pie

noun

pies plural

1. printing types mixed together indiscriminately.

2. any confused mixture; jumble.

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verb (used with object)

pied, piing

1. to reduce (printing types) to a state of confusion.

2. to jumble.

PI ³ American  

1. Law. personal injury.

2. principal investigator.

3. Also P.I., p.i. private investigator.

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Pi. ⁴ American  

Or pi.

abbreviation

1. piaster.

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P.I. ⁵ American  

abbreviation

1. Philippine Islands.

2. Also PI, p.i. private investigator.

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pi ¹ British  

/ paɪ /

noun

1. a jumbled pile of printer's type

2. a jumbled mixture

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verb

1. to spill and mix (set type) indiscriminately

2. to mix up

pi ² British  

/ paɪ /

noun

1. the 16th letter in the Greek alphabet (Π, π), a consonant, transliterated as p

2. maths a transcendental number, fundamental to mathematics, that is the ratio of the circumference of a circle to its diameter. Approximate value: 3.141 592…; symbol: π

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PI ³ British  

abbreviation

1. Philippine Islands

2. private investigator

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pi ⁴ British  

/ paɪ /

adjective

1. slang short for pious pious

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pi Scientific  

/ pī /

1. An irrational number that has a numerical value of 3.14159265358979… and is represented by the symbol π. It expresses the ratio of the circumference to the diameter of a circle and appears in many mathematical expressions.

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pi Cultural  

1. The irrational number obtained by dividing the length of the diameter of a circle into its circumference. Pi is approximately 3.1416. The sign for pi is π.

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Other Word Forms

Noun Inflected Forms

• pies
  plural
• pis
  plural

Etymology

Origin of pi¹

First recorded in 1835–45; from Greek pî, peî, used in mathematics to represent Greek periphérion periphery ( def. )

Origin of pi²

First recorded in 1650–60; origin uncertain

Explanation

In math, pi is the ratio of a circle's circumference to its diameter. No matter how large or small a circle is, this ratio will always equal pi, or approximately 3.14. Although it sounds just like pie, this kind of pi isn't a delicious dessert with a pastry crust. Instead, it's an irrational number, one that can't be written as a simple fraction but instead goes on infinitely after the decimal point. Rounded to 3.14, it's close enough to help you calculate the diameter, radius, or area of a circle in your geometry class. Pi is an abbreviation of the Greek periphereia, "periphery."

Example Sentences

NBC has scheduled fresh episodes of five scripted dramas, including "Magnum P.I.," newcomer "Found" and a Canadian series, "Transplant."

From Reuters • Sep. 7, 2023

About 200 fans - wearing mustaches, sunglasses, Hawaiian shirts and Tigers caps - attended the game as part of Magnum P.I.

From Washington Times • Aug. 28, 2023

Stevens worked in television, too, on series such as Murder She Wrote and Magnum, P.I.

From BBC • Feb. 17, 2023

Mason’s war experiences and time spent observing others as a P.I. “give him a sort of empathy for the world,” Rhys said.

From Los Angeles Times • Jun. 9, 2021

When Eleanor rang the doorbell, Magnum, P.I., answered.

From "Eleanor & Park" by Rainbow Rowell

Related Words

• inquiry agent
• private detective
• private dick
• private eye
• private investigator
• sleuth