Go slow island (4)
I believe the answer is:
inch
I believe this is a double definition.
'go slow' is the first definition.
(thesaurus)
'island' is the second definition.
(I've seen this before)
(Other definitions for inch that I've seen before include "Move slowly and cautiously" , "Move by small amounts" , "Imperial measure" , "Progress slowly" , "One-twelfth of a foot" .)