Sound surprised as gaps develop (4)
I believe the answer is:
gasp
'sound' is the definition.
(I have seen 'Sound of astonishment' mean 'gasp' so perhaps 'sound' could also mean 'gasp')
'surprised as gaps develop' is the wordplay.
'gaps' can be anagrammed to 'GASP'.
But, I am unsure how the anagram is indicated.
Can you help me to learn more?
(Other definitions for gasp that I've seen before include "Convulsive breath" , "Draw breath sharply" , "Have trouble breathing" , "Show amazement" , "Utter breathlessly" .)