1. Showing the cunning, ingenuity or wickedness typical of a devil
   "devilish schemes";
   - diabolic, diabolical, mephistophelian, mephistophelean
    
2. Playful in an appealingly bold way
   "a devilish grin";
   - rascally, roguish

1. In a playfully devilish manner
   "He grinned devilish as he planned his next prank";
   - devilishly

See also: evil, ludic [formal], playful

Encyclopedia: Devilish