Actually, in fact (6)
I believe the answer is:
really
I believe this clue is a double definition.
'actually' is the first definition.
(I know that actually can be written as really)
'in fact' is the second definition.
(synonyms)
(Other definitions for really that I've seen before include "In genuine way" , "surprised expression" , "Actually, no kidding" , "Genuinely" , "Well I never!" .)