A singer married on an island (5)
I believe the answer is:
melba
'a singer' is the definition.
(I know that Melba is a coloratura soprano)
'married on an island' is the wordplay.
'married' becomes 'm' (abbreviation, e.g. in genealogy).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'an island' becomes 'elba' (Italian island).
'm'+'elba'='MELBA'
(Other definitions for melba that I've seen before include "Australian operatic soprano, d. 1931" , "Famous soprano" , "Dame Nellie --, Australian soprano" , "great soprano" , "Onslaught" .)