St. Columba's island (4)
I believe the answer is:
iona
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">st columba's island</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for iona that I've seen before include "inch" , "Island west of Mull" , "Hebridean isle" , "part of Scotland" , "Scottish island of ancient saints" .)