Nick quietly leaves island (4)
I believe the answer is:
inch
'island' is the definition.
(inch can mean a small island)
'nick quietly leaves' is the wordplay.
'nick' becomes 'pinch' (both can mean steal).
'quietly' becomes 'p' (p for piano and quiet).
'leaves' is a deletion indicator.
'pinch' with 'p' taken away is 'INCH'.
(Other definitions for inch that I've seen before include "Creep, edge" , "Crawl; imperial measurement" , "no great length" , "Fraction of a foot" , "Move very slowly - a very short distance" .)