One part of Ireland supports Ring composer (7)
I believe the answer is:
bellini
'composer' is the definition.
(I know that Bellini is a composer)
'one part of ireland supports ring' is the wordplay.
'one' becomes 'i' (Roman numeral).
'part of ireland' becomes 'NI' (Northern Ireland).
'supports' means one lot of letters go next to another (bottom letters provide a support for the top ones).
'ring' becomes 'bell' (both can mean to call on the phone).
'i'+'ni'='ini'
'ini' put after 'bell' is 'BELLINI'.
(Other definitions for bellini that I've seen before include "drink" , "Peach juice cocktail" , "Cocktail; painter; opera composer" , "member of painting family" , "Italian opera composer (Norma)" .)