Unbelievable (10)
'unbelievable' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for incredible that I've seen before include "Unbelievable" , "Fantastic" , "Beyond belief" , "Impossible to believe" .)
(Other definitions for wow that I've seen before include "Exclamation of surprise or praise - a palindrome" , "Palindrome exclamation of astonishment or admiration" , "Cor! - huge success" , "Great success" , "that's incredible!" .)
(Other definitions for i say that I've seen before include "Look here; oh, my" , "Comment from protestor" , "Good heavens!" , "Dear me!" , "Blimey!" .)