International organisation raising moose youngster to be free (8)
I believe the answer is:
unbuckle
'be free' is the definition.
(thesaurus)
'international organisation raising moose youngster' is the wordplay.
'international organisation' becomes 'UN' (United Nations).
'raising' is a reversal indicator (in a down clue, letters go up).
'moose' becomes 'elk' (synonyms).
'youngster' becomes 'cub' (cub can mean a young person).
'elk'+'cub'='elkcub'
'elkcub' back-to-front is 'buckle'.
'un'+'buckle'='UNBUCKLE'
'to' is the link.
(Other definitions for unbuckle that I've seen before include "Release from a belt or shoe, perhaps" , "Undo (a shoe?)" , "Undo sandals" .)