Destroy Scottish island — no small island (4)
I believe the answer is:
'destroy' is the definition.
(I've seen this before)
'scottish island no small island' is the wordplay.
'scottish island' becomes 'islay' (island of the Hebrides).
'no' is a deletion indicator.
'small island' becomes 'i' (abbreviation or 'small' form for island).
'islay' with 'i' taken out is 'SLAY'.
(Other definitions for slay that I've seen before include "Fatally hit" , "Massacre" , "Kill with premeditation" , "Kill, murder" , "Destroy" .)