Dive exercises to include breathing apparatus? (6)
I believe the answer is:
plunge
'dive' is the definition.
(synonyms)
'exercises to include breathing apparatus?' is the wordplay.
'exercises' becomes 'pe' (Physical Education).
'to include' means one lot of letters goes inside another.
'breathing apparatus?' becomes 'lung' (I've seen this in another clue).
'pe' enclosing 'lung' is 'PLUNGE'.
(Other definitions for plunge that I've seen before include "Thrust or dive into" , "Sudden fall" , "Dive or swoop" , "Pitch" , "A steep drop" .)