pi

1 of 5

noun (1)

ˈpī 

plural pis ˈpīz 

1

: the 16th letter of the Greek alphabet see Alphabet Table

2

a

: the symbol π denoting the ratio of the circumference of a circle to its diameter

b

: the ratio itself : a transcendental number having a value rounded to eight decimal places of 3.14159265

pi

2 of 5

noun (2)

ˈpī 

variants or less commonly pie

plural pies

1

: type that is spilled or mixed

2

: a pi character or matrix

pi

3 of 5

verb

variants or less commonly pie

pied; piing or pieing

transitive verb

: to spill or throw (type or type matter) into disorder

intransitive verb

: to become pied

pi

4 of 5

adjective

variants or less commonly pie

1

: not intended to appear in final printing

pi lines

2

: capable of being inserted only by hand

pi characters

PI

5 of 5

abbreviation

1

Philippine Islands

2

private investigator

3

programmed instruction

Examples of pi in a Sentence

Recent Examples on the Web

Noun

As immutable as pi is, so is Pi (π) Day, a celebration that San Francisco’s Exploratorium invented back in 1988 that has become an international sensation. —Randy McMullen, The Mercury News, 13 Mar. 2025

March 14 is also known as National Pi Day—a celebration of the mathematical constant π (pi). —Raja Krishnamoorthi, Newsweek, 13 Mar. 2025

Unlike the more familiar real numbers – positive and negative integers, fractions, square roots, cube roots and even numbers such as pi – complex numbers have an imaginary component. —William Ross, The Conversation, 10 Mar. 2025

Moore equipped his pinball machine setup with the flexibility of a computer — one arrangement of bumpers might calculate the first thousand digits of pi, and another might compute the best next move in a game of chess. —Charlie Wood, Quanta Magazine, 7 Mar. 2025

Word History

Etymology

Noun (1)

Middle Greek, from Greek pei, of Semitic origin; akin to Hebrew pē pe

Noun (2)

origin unknown

First Known Use

Noun (1)

15th century, in the meaning defined at sense 1

Noun (2)

circa 1659, in the meaning defined at sense 1

Verb

1889, in the meaning defined at transitive sense

Adjective

circa 1940, in the meaning defined at sense 1

Phrases Containing pi

• pi-meson

Rhymes for pi

• ai
• aye
• bae
• bi
• buy
• by
• bye
• chai
• chi
• cry
• die
• dry

Kids Definition

pi

noun

ˈpī

plural pis

ˈpīz

1

: the 16th letter of the Greek alphabet

—Π or π

2

a

: the symbol π representing the ratio of the circumference of a circle to its diameter

b

: the ratio itself having a value of approximately 3.1416

Legal Definition

P&I

1 of 2 abbreviation

principal and interest

PI

2 of 2 abbreviation

private investigator