Diving gear from South Island (5)
I believe the answer is:
scuba
'diving gear' is the definition.
(I've seen this in another clue)
'south island' is the wordplay.
'south' becomes 's' (abbreviation).
'island' becomes 'Cuba' (Cuba is an example).
's'+'cuba'='SCUBA'
'from' acts as a link.
(Other definitions for scuba that I've seen before include "Apparatus for divers" , "breather" , "Diving equipment" , "Sort of diver" , "Aqualung" .)