Islands or island spanning North (6)
I believe the answer is:
orkney
'islands' is the definition.
(I've seen this before)
'or island spanning north' is the wordplay.
'island' becomes 'key' (key can mean an island or reef).
'spanning' means one lot of letters goes inside another.
'north' becomes 'N' (abbreviation).
'key' placed around 'n' is 'kney'.
'or'+'kney'='ORKNEY'
(Other definitions for orkney that I've seen before include "Islands off north coast of Scotland" , "Islands across Pentland Firth" , "The ...... Islands are off NE Scotland" , "The ...... Islands are off NEcorner of Scotland" , "Scottish archipelago" .)