Move gradually - Irish island (4)
I believe the answer is:
inch
This clue is a double definition.
'move gradually' is the first definition.
(I've seen this in another clue)
'irish island' is the second definition.
(I've seen this before)
(Other definitions for inch that I've seen before include "See 12" , "Move forward slowly and carefully" , "... or not so long < , Celtic island" , "Part of a foot" , "Two point five four cm" .)