Awfully, frightfully (8)
I believe the answer is:
terribly
This clue is a double definition.
'awfully' is the first definition.
(I know that awfully can be written as terribly)
'frightfully' is the second definition.
(I know that frightfully can be written as terribly)
(Other definitions for terribly that I've seen before include "Awfully, frightfully" , "In an awful manner" , "In a dreadful manner" , "Very badly" .)