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.
-
Mathematics.
-
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
-
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
abbreviation
-
Philippine Islands
-
private investigator
pi
3
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
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:
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
Ramanujan's methods became foundational to modern mathematical and computational approaches for calculating pi, including those used by today's most advanced machines.
From Science Daily ● Dec. 16, 2025
That approaches but still falls short of the classically modeled pentacene and its 22 pi electrons.
From Science Magazine ● May 30, 2024
It’s similar to the way Adah will sometimes turn up knowing some entire, difficult thing like French or the square root of pi when I’d been taking for granted I knew everything she did.
From "The Poisonwood Bible" by Barbara Kingsolver
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
"Our team achieved a single-channel transmission rate of 240 gigabits per second," says Tadao Nagatsuma, PI of the project.
From Science Daily ● Feb. 1, 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
He really did look an awful lot like Magnum, PI.
From "Eleanor & Park" by Rainbow Rowell
“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
“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
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
Rush’s decades-long career also includes films “Taza, Son of Cochise,” “Magnificent Obsession” and “Hombre,” and TV series “Magnum, P.I., “
From Los Angeles Times ● Apr. 1, 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
When Eleanor rang the doorbell, Magnum, P.I., answered.
From "Eleanor & Park" by Rainbow Rowell
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
The now elusive species was once common and frequently caught in the River Thames to make eel pies and jellied eels.
From BBC ● Jul. 3, 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
Inside, the joints feature coal- or wood-fired ovens; pizzaioli, like priests, ritually pass their hands over the pies.
From The Wall Street Journal ● May 22, 2026
At least it was Thursday; the twins would be eating pies at Wash’s house and so would come home happy.
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
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
Mom—I'm ok, just need ONE mental-health day. see you later and pis don’t worry at ALL.
From "Goodbye Stranger" by Rebecca Stead
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
I walked down the street like the pied piper, it was awesome.
From BBC ● Jan. 8, 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
She asked him why he needed to know that, and he told her that Doug Swieteck’s brother was in his office at that very moment for having called Mr. Ludema a pied ninny.
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.
