Scottish island (4)
(Other definitions for iona that I've seen before include "Holy island" , "place in the Hebrides" , "Hebridean island associated with St Columba" , "Isolated part of UK" , "Site of St Columba's monastery" .)
'scottish island' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for skye that I've seen before include "Destination of a princely boat trip" , "Island in a boat song about Flora MacDonald and Bonnie Prince Charlie" , "Scottish location" , "Largest isle of the Inner Hebrides" , "Isle; terrier type" .)