pi
noun
the 16th letter of the Greek alphabet (Π, π).
pi
1 American
[pahy]
/ paɪ /
noun
-
pis
plural
-
the 16th letter of the Greek alphabet (Π, π).
-
the consonant sound represented by this letter.
-
Mathematics.
-
the letter π, used as the symbol for the ratio of the circumference of a circle to its diameter.
-
the ratio itself: 3.141592+.
-
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
-
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
-
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
2
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
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
In recent decades, advances in computing have pushed this familiar constant far beyond the classroom, with powerful supercomputers now calculating pi to trillions of decimal places.
From Science Daily ● Dec. 16, 2025
They made a list of all the famous players from each of the teams, then added pi to each famous player’s jersey number, but didn’t know what to look for after that.
From "The Parker Inheritance" by Varian Johnson
Shares, which trade under the ticker PI, dropped 5.3% to $189 ahead of the opening bell.
From Barron's ● Jan. 14, 2026
When Minnie Polson comes to the duo’s PI agency seeking help, things go south after an ill-timed remark causes her to storm out.
From Los Angeles Times ● May 15, 2024
Alexandre Harari is a PI in the Hi-TIDe team at Ludwig Lausanne and an associate professor at the University of Lausanne.
From Science Daily ● May 7, 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
Just after 6:48 a.m., when the 911 call first came in, the dispatcher called out a 10-50 PI, a personal injury accident, and the coordinates.
From "A Deadly Wandering: A Mystery, a Landmark Investigation, and the Astonishing Science of Attention in the Digital Age" by Matt Richtel
“Yeah, this is Pi. Can we keep him, please?”
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
“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
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
“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
“What I loved about it was, it’s a way of doing a P.I. show that didn’t require rebooting something,” Olin says.
From Los Angeles Times ● Feb. 9, 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
However, he did guest star in an two episodes of the revived Magnum P.I., which launched in 2018, starring Jay Hernandez and Perdita Weeks.
From BBC ● Aug. 8, 2022
When Eleanor rang the doorbell, Magnum, P.I., answered.
From "Eleanor & Park" by Rainbow Rowell
Organic food company Amy’s Kitchen, which started selling frozen pot pies nearly 40 years ago, recently rolled out family-size options for meals like vegetable lasagna, cheese enchiladas and pad thai.
From The Wall Street Journal ● Sep. 17, 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
Around her are patio tables displaying the kind of food the shop carried: pies and cakes, what appear to be stuffed tomatoes, baguettes, sophisticated deli salads, gorgeous hunks of cheese.
From Salon ● Jul. 11, 2026
Shetland has plenty of honesty boxes - filled with fresh eggs, home baking and even pies.
From BBC ● May 31, 2026
He cocked an eyebrow at the twins, who nibbled at the crimped edge of the pies with a look of determined caution.
From "Out of Darkness" by Ashley Hope Pérez
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
“You are a pied ninny,” said Danny Hupfer.
From "The Wednesday Wars" by Gary D. Schmidt
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
