Whisky required by a Mediterranean island (5)
I believe the answer is:
malta
'mediterranean island' is the definition.
(Malta is an island in the Mediterranean)
'whisky required by a' is the wordplay.
'whisky' becomes 'malt' (malt whisky is a kind of whisky).
'required by' says to put letters next to each other.
'malt'+'a'='MALTA'
(Other definitions for malta that I've seen before include "seagirt republic" , "The capital is Valetta" , "GC island" , "Mediterranean island state" , "small island" .)