Greek island initially shocking Hebrew prophet (5)
I believe the answer is:
samos
'greek island' is the definition.
(Samos is a Greek island)
'initially shocking hebrew prophet' is the wordplay.
'initially' says to take the initial letters.
'hebrew prophet' becomes 'amos' (I've seen this in another clue).
The initial letter of 'shocking' is 's'.
's'+'amos'='SAMOS'
(Other definitions for samos that I've seen before include "somewhere in the Aegean" , "Aegean Sea island" , "birthplace of Pythagoras" , "Greek island?" .)