pieyoudaoicibaDictYouDict[pie 词源字典]
pie: [14] The characteristic feature of pies in the Middle Ages was that their filling consisted of a heterogeneous mixture of ingredients (as opposed to pasties, which had just one main ingredient). This has led etymologists to suggest that pies were named after magpies (or pies, as they were originally called), from a supposed resemblance between the miscellaneous contents of pies and the assortment of objects collected by thieving magpies.

Although pie has now been superseded by magpie as the bird-name, it survives in pied [14] (etymologically ‘coloured black and white like a magpie’) and piebald [16] (etymologically ‘streaked with black and white’).

=> magpie, pied, piebald[pie etymology, pie origin, 英语词源]
pie (n.1)youdaoicibaDictYouDict
"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)youdaoicibaDictYouDict
"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)youdaoicibaDictYouDict
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); compare pica (n.1). As a verb from 1870. Related: Pied.