# pi

^{1}pi

*noun*\ËˆpÄ«\

*plural*

**pis**\ËˆpÄ«z\

## Definition of *PI*

1

**:**Â the 16th letter of the Greek alphabet â€” see alphabet table

2

*a*

**:**Â the symbol Ï€ denoting the ratio of the circumference of a circle to its diameter

*b*

**:**Â the ratio itself

**:**Â a transcendental number having a value rounded to eight decimal places of 3.14159265

## Origin of *PI*

Middle Greek, from Greek

*pei,*of Semitic origin; akin to Hebrew*pÄ“*peFirst Known Use: 1638

^{2}pi

*noun*\ËˆpÄ«\

*plural*

**pies**

## Definition of *PI*

1

**:**Â type that is spilled or mixed

2

**:**Â a pi character or matrix

## Variants of *PI*

**pi**also

**pie**\ËˆpÄ«\

## Origin of *PI*

origin unknown

First Known Use: circa 1659

^{3}pi

*verb*

**pied**

**pi·ing**

*or*

**pie·ing**

## Definition of *PI*

transitive verb

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

intransitive verb

**:**Â to become pied

## Variants of *PI*

**pi**also

**pie**

## First Known Use of *PI*

1889

^{4}pi

*adjective*

## Definition of *PI*

1

**:**Â not intended to appear in final printing <

*pi*lines>

2

**:**Â capable of being inserted only by hand <

*pi*characters>

## Variants of *PI*

**pi**also

**pie**

## First Known Use of *PI*

circa 1940

## PI

*abbreviation*

## Definition of *PI*

1

Philippine Islands

2

private investigator

3

programmed instruction

## pi

*noun*

*(Concise Encyclopedia)*

In mathematics, the ratio of the circumference of a circle to its diameter. An irrational number (*see also* transcendental number), it has an approximate value of 3.14, but its exact value must be represented by a symbol, the Greek letter . Pi is used in calculations involving lengths, areas, and volumes of circles, spheres, cylinders, and cones. It also arises frequently in problems dealing with certain periodic phenomena (e.g., motion of pendulums, alternating electric currents). By the end of the 20th century, computers had calculated pi to more than 200 billion decimal places.

## Learn More About *PI*

## Browse

**Ask The Editor** Videos

## Seen & Heard

What made you want to look up *pi*? Please tell us where you read or heard it (including the quote, if possible).