Diving apparatus (5)
I believe the answer is:
scuba
'diving apparatus' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for scuba that I've seen before include "Device that lets divers breathe under water" , "Apparatus for divers" , "Diving apparatus" , "Diving equipment" , "Self-contained underwater breathing apparatus (acronym)" .)