pi
noun
the 16th letter of the Greek alphabet (Π, π).
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piing.
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.
-
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
-
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
abbreviation
-
Philippine Islands
-
private investigator
pi
3
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
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
Under the right conditions, neodymium and dioxygen formed pi interactions that had previously been considered unlikely.
From Science Daily ● Jul. 29, 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
It was a very short conversation, however, because I cut him off by asking him to recite pi to the sixth digit, claiming it was an entrance requirement, regardless of the shoes.
From "Geeks: How Two Lost Boys Rode the Internet Out of Idaho" by Jon Katz
Part essay, part documentary archive, it chronicled the discoveries she made as a private investigator and her attempt to renew her PI license that fall.
From Los Angeles Times ● Jul. 7, 2026
Shares, which trade under the ticker PI, dropped 5.3% to $189 ahead of the opening bell.
From Barron's ● Jan. 14, 2026
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
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
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
But Mosley's most high-profile role was in Magnum P.I., which saw him appear in 158 out of 162 episodes between 1980 and 1988.
From BBC ● Aug. 8, 2022
When Eleanor rang the doorbell, Magnum, P.I., answered.
From "Eleanor & Park" by Rainbow Rowell
If you want a piece of pies like this one, it would be useful to know as much about human nature as possible.
From The Wall Street Journal ● Sep. 10, 2026
He declines to share details but the contraption will make square pan-style pies and that the machine is inspired by the way 3D printers work.
From BBC ● Aug. 27, 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
While Papa made the pies, Hanako would read a book in the office with Sadie.
From "A Place to Belong" by Cynthia Kadohata
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
The trust said pied tamarins required "stress-free environments and specialist care"
From BBC ● Nov. 6, 2026
When the pied piper loses his audience, we must ask whether the people have rediscovered their conscience or simply found a new tune to follow.
From Salon ● Nov. 5, 2026
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 took on this odd role of being the pied piper of bocce,” he said.
From Los Angeles Times ● Jul. 1, 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
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