Source : Webster's Revised Unabridged Dictionary (1913)

Pretty \Pret"ty\, a. [Compar. {Prettier}; superl. {Prettiest}.]
   [OE. prati, AS. pr[ae]ttig, pr[ae]tig, crafty, sly, akin to
   pr[ae]t, pr[ae]tt, deceit, trickery, Icel. prettugr tricky,
   prettr a trick; probably fr. Latin, perhaps through Celtic;
   cf. W. praith act, deed, practice, LL. practica execution,
   practice, plot. See {Practice}.]
   1. Pleasing by delicacy or grace; attracting, but not
      striking or impressing; of a pleasing and attractive form
      a color; having slight or diminutive beauty; neat or
      elegant without elevation or grandeur; pleasingly, but not
      grandly, conceived or expressed; as, a pretty face; a
      pretty flower; a pretty poem.

            This is the prettiest lowborn lass that ever Ran on
            the greensward.                       --Shak.

   2. Moderately large; considerable; as, he had saved a pretty
      fortune. ``Wavering a pretty while.'' --Evelyn.

   3. Affectedly nice; foppish; -- used in an ill sense.

            The pretty gentleman is the most complaisant in the
            world.                                --Spectator.

   4. Mean; despicable; contemptible; -- used ironically; as, a
      pretty trick; a pretty fellow.

   5. Stout; strong and brave; intrepid; valiant. [Scot.]

            [He] observed they were pretty men, meaning not
            handsome.                             --Sir W.
                                                  Scott.

   Syn: Elegant; neat; fine. See {Handsome}.

Source : WordNet®

pretty
     adj 1: pleasing by delicacy or grace; not imposing; "pretty girl";
            "pretty song"; "pretty room"
     2: (used ironically) unexpectedly bad; "a pretty mess"; "a
        pretty kettle of fish"
     [also: {prettied}, {prettiest}, {prettier}]

pretty
     adv : used as an intensifier (`jolly' is used informally in
           Britain); "pretty big"; "pretty bad"; "jolly decent of
           him" [syn: {jolly}]
     [also: {prettied}, {prettiest}, {prettier}]

prettiest
     See {pretty}