Prone, apt (to) (6)
I believe the answer is:
likely
I believe this is a double definition.
'prone' is the first definition.
(thesaurus)
'apt to' is the second definition.
(thesaurus)
(Other definitions for likely that I've seen before include "On the cards" , "In prospect" , "In all probability" , "Probable, expected" , "Promising; probable" .)