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

Whether tangent, square root, pi or exponentiation, all these functions can be encoded using only the number 1 and the operator eml(x,y) = exp(x) − ln(y). — Manon Bischoff, Scientific American, 3 Nov. 2026

Pi also stands for powerful machines Although pi itself will never run out of digits, the race to calculate them keeps pushing computing technology forward. — Rupendra Brahambhatt, Interesting Engineering, 15 Mar. 2026

Even squares or irregular blobs can be broken down into a series of progressively smaller circles and calculated using pi, Davoyan said. — ABC News, 14 Mar. 2026

March 14 is the date that otherwise rational people celebrate this irrational number, because 3/14 contains the first three digits of pi. — Rhett Allain, Wired News, 14 Mar. 2026

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

1846, in the meaning defined at transitive sense

Adjective

1871, 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