Middle English pratie "cunning, crafty, clever" (c. 1300 as a surname), from Old English prættig (West Saxon), pretti (Kentish), *prettig (Mercian) "cunning, skillful, artful, wily, astute," from prætt, *prett "a trick, wile, craft," from Proto-Germanic *pratt- (source also of Old Norse prettr "a trick," prettugr "tricky;" Frisian pret, Middle Dutch perte, Dutch pret "trick, joke," Dutch prettig "sportive, funny," Flemish pertig "brisk, clever"), a word of unknown origin.
The connection between the Old English and Middle English words "has several points of obscurity" [OED], and except in surnames there is no record of it 13c.-14c., but they generally are considered the same. The meaning had expanded by c. 1400 to "manly, gallant," also "ingeniously or cleverly made," to "fine, pleasing to the aesthetic sense," to "beautiful in a slight way" (mid-15c.). Also used of bees (c. 1400). For sense evolution, compare nice, silly, neat (adj.), fair (adj.).
Pretty applies to that which has symmetry and delicacy, a diminutive beauty, without the higher qualities of gracefulness, dignity, feeling, purpose, etc. A thing not small of its kind may be called pretty if it is of little dignity or consequence: as a pretty dress or shade of color; but pretty is not used of men or their belongings, except in contempt. [Century Dictionary, 1897]
Of things, "fine, pleasing" 1560s. Ironical use is from 1530s (compare ironical use of fine (adj.)). The meaning "not a few, considerable, moderately large in quantity, number, extent, or duration" is from late 15c. Pretty please as an emphatic plea is attested from 1902. A pretty penny "lot of money" is recorded from 1703.
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. 
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]