Song about one island wine (7)
I believe the answer is:
chianti
'wine' is the definition.
(Chianti is an example)
'song about one island' is the wordplay.
'song' becomes 'chant' (song sung by a crowd).
'about' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'island' becomes 'i' (geographical abbreviation).
'chant' enclosing 'i' is 'chiant'.
'chiant'+'i'='CHIANTI'
(Other definitions for chianti that I've seen before include "Italian offering" , "Italian wine - mountain range" , "Tuscan red wine" , "Italian wine variety" , "I can hit (anag) - alcoholic drink" .)