Talk, gasping noiselessly! (3)
I believe the answer is:
gas
'talk' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for gas that I've seen before include "See 2" , "Domestic fuel" , "Carbon dioxide, say" , "Oxygen is one" , "It may be natural" .)