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).
"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.
"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."
n. pl. pis
Symbol π The 16th letter of the Greek alphabet.
The pH value for the isoelectric point of a given substance in solution.