Extremely stark, the old Hebridean island (4)
I believe the answer is:
skye
'hebridean island' is the definition.
(I've seen this before)
'extremely stark the old' is the wordplay.
'extremely' says to hollow out the word (remove centre letters).
'the old' becomes 'ye'.
'stark' with its middle removed is 'sk'.
'sk'+'ye'='SKYE'
(Other definitions for skye that I've seen before include "Largest Inner Hebridean island" , "Home of the Cuillin mountains" , "Island in a boat song about Flora MacDonald and Bonnie Prince Charlie" , "Largest isle of the Inner Hebrides" , "somewhere off Scotland's west coast" .)