Young girl south of island (5)
I believe the answer is:
issue
'young' is the definition.
(thesaurus)
'girl south of island' is the wordplay.
'girl' becomes 'sue'.
'south of' means one lot of letters go next to another.
'island' becomes 'is'.
'sue' put after 'is' is 'ISSUE'.
(Other definitions for issue that I've seen before include "Give out; children" , "Offspring, or the point in question" , "Emanate" , "Question in dispute to be settled" , "Important topic for offspring" .)