Characters with current breathing apparatus (3,3)
I believe the answer is:
air sac
'breathing apparatus' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'characters with current' is the wordplay.
I cannot really understand how this works, but
'current' could be 'air' (a current of air) and 'air' is found in the answer.
The remaining letters 'sac' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for air sac that I've seen before include "Lung compartment" , "Part of a lung" , "Alveolus" .)