Whisky first of all for Mediterranean island (5)
I believe the answer is:
malta
'for mediterranean island' is the definition.
(Malta is an island in the Mediterranean)
'whisky first of all' is the wordplay.
'whisky' becomes 'malt' (malt whisky is a kind of whisky).
'first of all' becomes 'a' (1st letter of 'all').
'malt'+'a'='MALTA'
(Other definitions for malta that I've seen before include "detached dwelling place" , "Island to the south of Sicily" , "Island member of the European Union" , "Island nation" , "Mediterranean island republic" .)