Likely but not certain (8)
I believe the answer is:
probable
'likely but not certain' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for probable that I've seen before include "Likely to happen but not certain" , "on the cards" , "Person most likely" , "Likely to be the case" , "Seeming to have a good chance of happening" .)