Source : Webster's Revised Unabridged Dictionary (1913)

Mischievous \Mis"chie*vous\, a.
   Causing mischief; harmful; hurtful; -- now often applied
   where the evil is done carelessly or in sport; as, a
   mischievous child. ``Most mischievous foul sin.'' --Shak.

         This false, wily, doubling disposition is intolerably
         mischievous to society.                  --South.

   Syn: Harmful; hurtful; detrimental; noxious; pernicious;
        destructive. -- {Mis"chie*vous*ly}, adv. --
        {Mis"chie*vous*ness}, n.

Source : WordNet®

mischievously
     adv : in a disobedient or naughty way; "he behaved badly in
           school"; "he mischievously looked for a chance to
           embarrass his sister"; "behaved naughtily when they had
           guests and was sent to his room" [syn: {badly}, {naughtily}]