Island of no great length? (4)
I believe the answer is:
inch
This clue is a double definition.
'island' is the first definition.
(inch can mean a small island)
'no great length?' is the second definition.
(I've seen this before)
'of' is the link.
(Other definitions for inch that I've seen before include "2.45 cm" , "0.0254 metre" , "Move very slowly - a very short distance" , "Progress slowly" , "Move along gradually" .)