Source : Webster's Revised Unabridged Dictionary (1913)

Dreadfully \Dread"ful*ly\, adv.
   In a dreadful manner; terribly. --Dryden.

Source : WordNet®

dreadfully
     adv 1: of a dreadful kind; "there was a dreadfully bloody accident
            on the road this morning" [syn: {awfully}, {horribly}]
     2: in a dreadful manner; "as he looks at the mess he has left
        behind he must wonder how the Brits so often managed to
        succeed in the kind of situation where he has so dismally
        failed" [syn: {dismally}]