Q, as usual has presented a stentorian reply... it may be of value to understand the devlopment of the word 'pretty'...
O.E. prættig (W.Saxon), *prettig (Mercian) "cunning, skillful, artful," from prætt, *prett "a trick, wile, craft," from W.Gmc. *pratt- (cf. O.N. prettr "a trick," prettugr "tricky;" Fris. pret, M.Du. perte, Du. pret "trick, joke," Du. prettig "sportive, funny," Flem. pertig "brisk, clever"). Connection between O.E. and M.E. 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.). For sense evolution, compare nice, silly. Used to qualify adjectives and adverbs ("moderately") since 1560s. As a verb (usually with up) it is attested from 1916. Prettily is from c.1400; prettify first recorded 1850. Pretty-boy is attested from 1885. A pretty penny "lot of money" is first recorded 1768. (Source: Online Etymology Dictionary)