Prophesy when fear has worn off (8)
I believe the answer is:
forewarn
'prophesy' is the definition.
(thesaurus)
'fear has worn off' is the wordplay.
'has' is a charade indicator (letters next to each other).
'off' indicates anagramming the letters.
'fear' after 'worn' is 'wornfear'.
'wornfear' is an anagram of 'FOREWARN'.
'when' acts as a link.
(Other definitions for forewarn that I've seen before include "urge caution?" , "Tip off" , "Give advance notice" , "alert" , "Caution in advance" .)