pi
noun
the 16th letter of the Greek alphabet (Π, π).
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pily.
pi
1 American
[pahy]
/ paɪ /
noun
-
pis
plural
-
the 16th letter of the Greek alphabet (Π, π).
-
the consonant sound represented by this letter.
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Mathematics.
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the letter π, used as the symbol for the ratio of the circumference of a circle to its diameter.
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the ratio itself: 3.141592+.
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pi
2
American
[pahy]
/ paɪ /
Or
pie
noun
-
pies
plural
-
printing types mixed together indiscriminately.
-
any confused mixture; jumble.
verb (used with object)
pied,
piing
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to reduce (printing types) to a state of confusion.
-
to jumble.
PI
3
American
Pi.
4
American
Or
pi.
abbreviation
P.I.
5
American
pi
1
British
/ paɪ /
noun
-
a jumbled pile of printer's type
-
a jumbled mixture
verb
-
to spill and mix (set type) indiscriminately
-
to mix up
pi
2
British
/ paɪ /
noun
-
the 16th letter in the Greek alphabet (Π, π), a consonant, transliterated as p
-
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
PI
3
British
abbreviation
-
Philippine Islands
-
private investigator
pi
4
British
/ paɪ /
adjective
pi
Scientific
/ pī /
pi
Cultural
Other Word Forms
Noun Inflected Forms
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."
Vocabulary lists containing pi
Pi Day Vocabulary
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Scrabble: Two-Letter Words
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Geometry - Middle School
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
See Examples For:
It frees a student from memorizing all formulas, such as pi to the fourth decimal, but not from knowing whether an answer is right, he said.
From Los Angeles Times ● Aug. 27, 2026
Sharp, who worked at the Greenwich Royal Observatory and has a crater on the moon named after him, was also a mathematician who calculated pi to 72 decimal places.
From BBC ● Apr. 1, 2026
In science-fiction scenarios of first contact with extraterrestrials, humans usually bootstrap a common language with mathematics, demonstrating that we know the digits of pi and so forth.
From The Wall Street Journal ● Jan. 9, 2026
These expressions were strikingly efficient, allowing pi to be computed much faster than existing techniques of the time.
From Science Daily ● Dec. 16, 2025
I close my eyes and recite the numbers of pi in my head. 3.14159265358979323846264338327950288419716...
From "The Miscalculations of Lightning Girl" by Stacy McAnulty
Shares, which trade under the ticker PI, dropped 5.3% to $189 ahead of the opening bell.
From Barron's ● Jan. 14, 2026
To build out an eight-episode series, Schur and the writers played up the theft at the retirement home to create more room for clues, cliffhangers and the PI character, played by Lilah Richcreek Estrada.
From Los Angeles Times ● Nov. 14, 2024
By 1970, with a partnership in a successful PI agency and a stable and happy family, Easy Rawlins is a changed and contented man.
From Los Angeles Times ● Jun. 19, 2024
Senior vice president at the PI, Dr Duncan French, acknowledges the UFC has a responsibility, not just to their own roster of between 650-670 fighters, but to those involved at a much lower level.
From BBC ● Nov. 15, 2023
“You’ll get an hour in your logbook, PI under training,” Dympna told Maddie over her shoulder as they crossed to the Anson.
From "Code Name Verity" by Elizabeth Wein
“Lucy, I know you can’t adopt Cutie Pi. I’ve seen you 2 together. If your family was able to take in a dog, he would have gone home with you weeks ago.”
From "The Miscalculations of Lightning Girl" by Stacy McAnulty
“It’s easy to figure out. Pi. The distance to the sun. Three hundred and sixty-five days. It comes out to twenty miles per second, give or take a bit.”
From "100 Sideways Miles" by Andrew Smith
Then he said, “Very well, Pi. Sit down. Next time you will ask permission before leaving your desk.”
From "Life of Pi" by Yann Martel
“Yeah, this is Pi. Can we keep him, please?”
From "The Miscalculations of Lightning Girl" by Stacy McAnulty
“I know we could find someone to adopt Pi. We will put him on our blog. I bet he has 30 phone calls on the 1st day.”
From "The Miscalculations of Lightning Girl" by Stacy McAnulty
Even Charles’ goofier moments gleam with a satin elegance that scrapes against the no-nonsense manner of Estrada’s P.I.
From Salon ● Nov. 21, 2024
BBC Radio Wales pundits and former Wales strikers Helen Ward and Nathan Blake likened the 28-year-old's moustache to that of Magnum, P.I. actor Tom Selleck.
From BBC ● Mar. 24, 2024
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
When Eleanor rang the doorbell, Magnum, P.I., answered.
From "Eleanor & Park" by Rainbow Rowell
Some are exploring the specific needs of their communities to build revenue beyond pies and pints, offering book clubs, menopause fitness or ancient wassailing rituals.
From The Wall Street Journal ● Oct. 26, 2026
There, he entertained the great and the good with legendary parties, serving with champagne and shepherd's pies.
From BBC ● Oct. 5, 2026
Nicknamed "the Glooper" for his cries of "Gloop! Gloop!" after each strike, Godin spent more than three decades lobbing pies at rich and famous targets he felt needed bringing down a notch.
From Barron's ● Aug. 24, 2026
Standouts include the carnitas tacos and tamarind agua fresca at El Taco Torro, creative pies at Pizza Luna, house-smoked barbecue from Rollin Nolen’s BBQ, and Indian and Nepalese street food from Momo Dosa.
From Salon ● Jun. 11, 2026
They chose custard pies off the gleaming dessert cart.
From "Habibi" by Naomi Shihab Nye
He is content to address what he calls “a self-selected audience of intellectually upscale readers,” and if you don’t know what he means by “Pecksniffian Comstockery,” tant pis.
From Washington Post ● Sep. 23, 2021
But, as he may say now: tant pis.
From The Guardian ● Dec. 12, 2010
In halting English, a Moslem telegraph operator in the Middle East tapped out on the telex: "Is it correct Kennedy killed pis?"
From Time Magazine Archive
“Tant pis, the ceiling is a little low. One brisk hornpipe and we’d all be bashed stupid.”
From "The Astonishing Life of Octavian Nothing, Traitor to the Nation, Volume II: The Kingdom on the Waves" by M.T. Anderson
The picture is called The Sabine Women, and in the margin is scrawled: pim pis pit, pimus pistis pants.
From "The Handmaid's Tale" by Margaret Atwood
Meanwhile, the southern pied babbler does not, in fact, merely babble.
From Salon ● May 29, 2025
And when she got pied in the face at a press conference in Iowa—her instant response: “At least it’s a fruit pie”—a whole bunch of Americans reveled in her comeuppance.
From Slate ● Jan. 11, 2025
Articulate, charismatic and based in the host city of the next Paralympic Games, Frech has positioned himself to be the pied piper of the Paralympic movement for years.
From Los Angeles Times ● Aug. 29, 2024
Smith oozes upside, and he’s passionate about the Ducks — a bonus in that he could be a pied piper who attracts other recruits.
From Seattle Times ● Feb. 16, 2024
Pigeons could be made to look like roosters and peacocks, and dogs made short-haired, long-haired, pied, piebald, bowlegged, hairless, crop-tailed, vicious, mild-mannered, diffident, guarded, belligerent.
From "The Gene" by Siddhartha Mukherjee
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