Member of youth organisation on a Caribbean island (4)
I believe the answer is:
cuba
'caribbean island' is the definition.
(I've seen this before)
'member of youth organisation on a' is the wordplay.
'member of youth organisation' becomes 'cub' (I can't justify this - if you can you should believe this answer much more).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'cub'+'a'='CUBA'
Can you help me to learn more?
(Other definitions for cuba that I've seen before include "Island country involved in a 1962 missile crisis" , "Country famous for its cigars" , "Hemingway's stamping-ground" , "Long rum-based drink" , "Caribbean country of cigars and rum?" .)