Source : Webster's Revised Unabridged Dictionary (1913)

Rascally \Ras"cal*ly\, a.
   Like a rascal; trickish or dishonest; base; worthless; --
   often in humorous disparagement, without implication of
   dishonesty.

         Our rascally porter is fallen fast asleep. --Swift.

Source : WordNet®

rascally
     adj 1: playful in an appealingly bold way; "a roguish grin" [syn: {devilish},
             {roguish}]
     2: lacking principles or scruples; "the rascally rabble"; "the
        tyranny of a scoundrelly aristocracy" - W.M. Thackaray;
        "the captain was set adrift by his roguish crew" [syn: {roguish},
         {scoundrelly}, {blackguardly}]