The Collaborative International Dictionary of English v.0.48:
Fearfully \Fear"ful*ly\, adv. In a fearful manner. [1913 Webster]WordNet (r) 3.0 (2006):
fearfully adv 1: in fear, "she hurried down the stairs fearfully" [ant: dauntlessly, fearlessly, intrepidly] 2: in an alarming manner; "they were fearfully attacked"