Pi

How to spell pi

2 letters · 1 syllable

How to pronounce pi

What does pi mean?

1. nounThe mathematical constant equal to the ratio of a circle's circumference to its diameter, roughly 3.14159.
2. nounThe sixteenth letter of the Greek alphabet, written as the symbol used for the mathematical constant.

Pi in a sentence

• The formula for the area of a circle multiplies pi by the radius squared.

• The equation uses the Greek letter pi as its symbol.

• The teacher asked the class to recite the first ten digits of pi.

• Members of the fraternity wore badges marked with the letter pi.

Where does pi come from?

Language of origin: Greek

Pi is simply the English name of the sixteenth letter of the Greek alphabet, written "\u03c0" in lower case, a name the Greeks took from a Phoenician letter. Its famous mathematical role began when writers chose \u03c0 to stand for the ratio of a circle's circumference to its diameter, the letter being picked because it is the first sound of the Greek words "periphereia" (periphery) and "perimetros" (perimeter), both meaning the distance measured around something. The Welsh mathematician William Jones first used the symbol this way in 1706, and the great Leonhard Euler adopted it soon after, which fixed it in mathematics for good. Because the English name is pronounced exactly like the baked dish "pie", the two words are constant homophones, and the very short spelling is what makes writers reach for the wrong one. Today pi names both the constant, roughly 3.14159, and the Greek letter itself.

How the word is built

• pi (English name of the Greek letter "\u03c0", itself from the Greek word for the letter)

Words that sound like pi

They sound the same but mean different things, so the meaning decides which spelling to write.

• pie: A baked dish with a pastry base or covering, filled with fruit, meat, or vegetables.