Dreadful; excellent (7)
I believe the answer is:
awesome
I believe this clue is a double definition.
'dreadful' is the first definition.
(I've seen this in another clue)
'excellent' is the second definition.
(I've seen this in another clue)
(Other definitions for awesome that I've seen before include "Inspiring reverence mixed with fear" , "Amazing (sl.)" , "Inspiring admiration or wonder" , "Portentous" , "Instilling wonder" .)