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
-
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:
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 1914, shortly before leaving Madras for Cambridge, renowned Indian mathematician Srinivasa Ramanujan published a paper presenting 17 different formulas for calculating pi.
From Science Daily ● Dec. 16, 2025
I don’t tell her the numbers are digits of pi.
From "The Miscalculations of Lightning Girl" by Stacy McAnulty
I chose Joe because I’m a PI at heart, and there’s a tennis background.
From Los Angeles Times ● Oct. 14, 2026
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
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
“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
“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
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
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
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
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
They’re basically mini apple pies or blueberry pies.
From The Wall Street Journal ● Jun. 1, 2026
Shetland has plenty of honesty boxes - filled with fresh eggs, home baking and even pies.
From BBC ● May 31, 2026
Inkling ignores me. “—there developed a shortage. All the squash growing among the glaciers was harvested by humans to cook into pies and serve with turkey.”
From "Invisible Inkling" by Emily Jenkins
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
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
A neo-traditionalist and pied piper for the New York downtown set, Keith and his nine lives most recently turned to Instagram after a stroke impaired his ability to speak.
From Los Angeles Times ● Dec. 17, 2025
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
The yellow daffadowndillies have burst into bloom, and the tiny cupped flowers of crocuses are spreading their pied blankets of white and purple.
From "Ophelia" by Lisa Klein
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