the letter π, used as the symbol for the ratio of the circumference of a circle to its diameter.

the ratio itself: 3.141592+.

Origin of pi

^{1}

1835–45; < Greekpî, peî; used in mathematics to represent Greekperiphérion periphery

pie

^{1}

[pahy]

noun

a baked food having a filling of fruit, meat, pudding, etc., prepared in a pastry-lined pan or dish and often topped with a pastry crust: apple pie; meat pie.

a layer cake with a filling of custard, cream jelly, or the like: chocolate cream pie.

a total or whole that can be divided: They want a bigger part of the profit pie.

an activity or affair: He has his finger in the political pie too.

the 16th letter in the Greek alphabet (Π, π), a consonant, transliterated as p

mathsa 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

Word Origin for pi

C18 (mathematical use): representing the first letter of Greek periphereiaperiphery

Greek letter, from Hebrew, literally "little mouth." As the name of the mathematical constant, from 1841 in English, used in Latin 1748 by Swiss mathematician Leonhart Euler (1707-1783), as an abbreviation of Greek periphereia "periphery." For the meaning "printer's term for mixed type," see pie (3).

pie

n.1

"pastry," mid-14c. (probably older; piehus "bakery" is attested from late 12c.), from Medieval Latin pie "meat or fish enclosed in pastry" (c.1300), perhaps related to Medieval Latin pia "pie, pastry," also possibly connected with pica "magpie" (see pie (n.2)) on notion of the bird's habit of collecting miscellaneous objects. Figurative of "something to be shared out" by 1967.

According to OED, not known outside English, except Gaelic pighe, which is from English. In the Middle Ages, a pie had many ingredients, a pastry but one. Fruit pies began to appear c.1600. Figurative sense of "something easy" is from 1889. Pie-eyed "drunk" is from 1904. Phrase pie in the sky is 1911, from Joe Hill's Wobbly parody of hymns. Pieman is not attested earlier than the nursery rhyme "Simple Simon" (c.1820). Pie chart is from 1922.

pie

n.2

"magpie," mid-13c. (late 12c. as a surname), from Old French pie (13c.), from Latin pica "magpie" (see magpie). In 16c., a wily pie was a "cunning person."

pie

n.3

also pi, printers' slang for "a mass of type jumbled together" (also pi, pye), 1650s, perhaps from pie (n.1) on notion of a "medley," or pie (n.2); cf. pica (n.1). As a verb from 1870. Related: Pied.

An irrational number that has a numerical value of 3.14159265358979… and is represented by the symbol π. It expresses the ratio of the circumference to the diameter of a circle and appears in many mathematical expressions.

The irrational number obtained by dividing the length of the diameter of a circle into its circumference. Pi is approximately 3.1416. The sign for pi is π.