Probably promising (6)
I believe the answer is:
likely
This clue is a double definition.
'probably' is the first definition.
(I know that probably can be written as likely)
'promising' is the second definition.
(similar in meaning)
(Other definitions for likely that I've seen before include "In prospect" , "Probable, expected" , "Such as well might happen" , "Quite possible" , "Has a good chance of being the case" .)