Peak in Ionian Islands seen from east (5)
I believe the answer is:
sinai
'peak' is the definition.
(Mount Sinai)
'in ionian islands seen from east' is the wordplay.
'in' indicates the answer is hidden within the clue.
'from east' shows that the letters should be reversed in order.
'ianis' is hidden within 'ionian islands seen'.
'ianis' backwards is 'SINAI'.
(Other definitions for sinai that I've seen before include "Mt. where Moses received 10 Commandments" , "Mount on which Moses received the Ten Commandments" , "Egyptian location" , "11 Across peninsula" , "place to receive instructions about behaviour" .)