WordWeb Online

1. As a devil; in an evil manner
   "his writing could be devilishly satiric"
   - diabolically, fiendishly
    
2. In a playfully devilish manner
   "the socialists are further handicapped if they believe that capitalists are not only wicked but also devilishly clever"
   - devilish
    
3. (used to intensify) extremely
   "she was devilishly in love"
   - madly, insanely, deadly, deucedly

See also: devilish