"size of printing type of about six lines to the inch" (12 point), 1580s, probably from pica, the name of a book of rules in the Church of England for determining holy days (late 15c. in Anglo-Latin). This is probably from Latin pica "magpie" (see pie (n.2)); the book so called perhaps from the color and the "pied" look of the old type on close-printed pages. The type size was that generally used to print ordinals.

popular name of a common bird of Europe, Asia, and America, known for its chattering, acquisitiveness, curiosity, and mimicry, c. 1600, earlier simply pie (mid-13c.).

The first element is Mag, nickname for Margaret, long used in proverbial and slang English for qualities associated generally with women, especially in this case "idle chattering" (as in Magge tales "tall tales, nonsense," early 15c.; also compare French margot "magpie," from Margot, pet form of Marguerite). The name Margaret, and its reduced forms Mag, Madge, diminutive Maggie, also has long been familiarly applied to birds. Pies were proverbial since Middle English for chattering (as were jays), hence the application of pie to a prattling gossip or tattler, also "sly person, informer" (late 14c.) and in 15c.-16c. a wily pie (or wyly pye) was "a cunning person."

The second element, pie, is the earlier name of the bird, from Old French pie, from Latin pica "magpie" (source also of Spanish pega), fem. of picus "woodpecker," from PIE root *(s)peik- "woodpecker, magpie" (source also of Umbrian peica "magpie," Sanskrit pikah "Indian cuckoo," Old Norse spætr, German Specht "woodpecker"); possibly from PIE root *pi-, denoting pointedness, of the beak. The application to pies might be because the magpie also has a long, pointed tail.

The birds are proverbial for pilfering and hoarding and for their indiscriminate appetites (see pica (n.2)); they can be taught to speak, and have been regarded since the Middle Ages as ill omens.

Whan pyes chatter vpon a house it is a sygne of ryghte euyll tydynges. [1507]

Divination by numbering magpies is attested from c. 1780 in Lincolnshire; the rhyme varies from place to place, the only consistency being that one is bad, two are good.

The councils which magpies appear to hold together, at particular seasons, commonly called "folkmotes," are associated in the minds of many with superstitious and ominous notions. The innocent objects of terror, while meeting together most probably for the purpose of choosing mates, are supposed to be conspiring and clubbing their wits, for the weal or woe of the inhabitants of the neighbouring village. If they are of an even number and carry on their cheerful, noisy chatter, it is supposed to betoken good to old and young—but if there is an odd magpie perched apart from the rest, silent, and disconsolate, the reverse of this is apprehended, and mischievous consequences are inevitably expected. [The Saturday Magazine, Jan. 23, 1841]

the hypothetical reconstructed ancestral language of the Indo-European family, by 1905. The time scale of the "language" itself is much debated, but a recent date proposed for it is about 5,500 years ago. 

1580s, from apple + pie; noted by 1893 as a typical American dish. Apple-pie bed as a name for a childish prank is recorded from 1781; supposedly from the way of making apple turnovers, but some think it a folk etymology of French nappe pliée "folded sheet."

Greek letter corresponding to the Roman P, from Phoenician, literally "little mouth." As the name of the mathematical constant for the ratio of the circumference of a circle to the diameter, from 1841 in English, used in Latin 1748 by Swiss mathematician Leonhard Euler (1707-1783), as an abbreviation of Greek periphereia "periphery." For the printer's term for mixed type (often spelled pi), see pie (3).

also potpie, "pie made by lining the inner surface of a pot with pastry and filling it with meat and seasoning and baking it," 1807, American English, from pot (n.1) + pie (n.).

1915, proprietary name (Corning Glass Works, Corning, N.Y.) of a type of hard, heat-resistant glass, an arbitrary coinage, in which advertisement writers and eager etymologists see implications of Greek pyr "fire" and perhaps Latin rex "king;" but the prosaic inventors say it was based on pie (n.1), because pie dishes were among the first products made from it. The -r-, in that case, is purely euphonious.

"pathological craving for substance unfit for food" (such as chalk), 1560s, from Medieval Latin pica "magpie" (see pie (n.2)), probably translating Greek kissa, kitta "magpie, jay," also "false appetite." The connecting notion may be the birds' indiscriminate feeding. Compare geophagy.

As the magpie eats young birds, here is the bird to keep the sparrows' numbers in check, for it will live in towns and close to dwellings—just the localities sparrows frequent. The magpie's appetite is omnivorous, and it is charged with at times killing weakly lambs, and varying its diet by partaking of grain and fruit; but I never at Home heard any complaints of this bird from the farmers, whilst the gamekeepers had not a good word for it. The bird will eat carrion, so if one were disturbed taking a meal from a dead lamb it would probably be blamed for its death, which may have occurred from natural causes. [A. Bathgate, "The Sparrow Plague and its Remedy," in Transactions of the New Zealand Institute, 1903]

also pick-axe, "tool used for breaking up and digging ground," especially a pick with a sharp point on one side of the head and a broad blade on the other, early 15c., folk etymology alteration (by influence of axe) of Middle English  picas, pikeis (mid-13c.), via Anglo-French piceis, Old French pocois (11c.) and directly from Medieval Latin picosa "pick," which is related to Latin picus "woodpecker" (see pie (n.2)).

"of two different colors, having spots or patches of white and black or another color," 1580s, formed from pie (n.2) "magpie" + bald in its older sense of "spotted, white;" in reference to the black-and-white plumage of the magpie. Hence, "of mixed character, heterogeneous, mongrel" (1580s). Properly only of black-and-white colorings (compare skewbald).