1. [adv]  (used as intensives) extremely; "she was madly in love"; "deadly dull"; "deadly earnest"; "deucedly clever"; "insanely jealous"
2. [adv]  in a playfully devilish manner; "the socialists are further handicapped if they believe that capitalists are not only wicked but also devilishly clever"
3. [adv]  as a devil; in an evil manner; "his writing could be diabolically satiric"

DEVILISHLY is a 10 letter word that starts with D.