'Frightfully' definitions:

Definition of 'frightfully'

From: WordNet
adverb
Used as intensifiers; "terribly interesting"; "I'm awful sorry" [syn: terribly, awfully, awful, frightfully]

Definition of 'Frightfully'

From: GCIDE
  • Frightfully \Fright"ful*ly\, adv. In a frightful manner; to a frightful dagree. [1913 Webster]