prettyyoudaoicibaDictYouDict[pretty 词源字典]
pretty: [OE] In Old English pretty (or prættig, as it was then) meant ‘clever’ in a bad sense – ‘crafty, cunning’. Not until the 15th century had it passed via ‘clever’, ‘skilfully made’, and ‘fine’ to ‘beautiful’. It was a derivative of prætt ‘trick, wile’, which came from a prehistoric West Germanic *pratt- (source also of Dutch part ‘trick’).
[pretty etymology, pretty origin, 英语词源]
pretty (adj.)youdaoicibaDictYouDict
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- (cognates: Old Norse prettr "a trick," prettugr "tricky;" Frisian pret, Middle Dutch perte, Dutch pret "trick, joke," Dutch prettig "sportive, funny," Flemish pertig "brisk, clever"), of unknown origin.

Connection between Old English and Middle English words is uncertain, but if they are the same, meaning had shifted by c. 1400 to "manly, gallant," and later moved via "attractive, skillfully made," to "fine," to "beautiful in a slight way" (mid-15c.). Ironical use from 1530s. For sense evolution, compare nice, silly. Also used of bees (c. 1400). "After the OE. period the word is unknown till the 15th c., when it becomes all at once frequent in various senses, none identical with the OE., though derivable from it" [OED].

Meaning "not a few, considerable" is from late 15c. With a sense of "moderately," qualifying adjectives and adverbs, since 1560s. Pretty please as an emphatic plea is attested from 1902. A pretty penny "lot of money" is first recorded 1768.
pretty (n.)youdaoicibaDictYouDict
"a pretty person or thing," 1736, from pretty (adj.).
pretty (v.)youdaoicibaDictYouDict
1916, usually with up, from pretty (adj.). Related: Prettied; prettying. Compare prettify.