Found 2 items, similar to fiendishly.
English → English (WordNet) Definition: fiendishly fiendishly adv : as a devil; in an evil manner; “his writing could be diabolically satiric” [syn: diabolically, devilishly]
English → English (gcide) Definition: Fiendishly Fiendish \Fiend"ish\, a. Like a fiend; diabolically wicked or cruel; infernal; malignant; devilish; hellish. -- Fiend"ish*ly, adv. -- Fiend"ish*ness, n. [1913 Webster]