Youngster in South Africa needs aqualung (5)
I believe the answer is:
scuba
'aqualung' is the definition.
(synonyms)
'youngster in south africa' is the wordplay.
'youngster' becomes 'cub' (I've seen this before).
'in' indicates putting letters inside.
'south africa' becomes 'sa' (abbreviation).
'cub' inserted within 'sa' is 'SCUBA'.
'needs' acts as a link.
(Other definitions for scuba that I've seen before include "Diving apparatus" , "Device that lets divers breathe under water" , "Diving equipment" , "Sort of diver" , "Aqualung" .)