A bouncy sort of sound (4)
I believe the answer is:
echo
'sound' is the definition.
(I know that echo is a more specific form of sound)
'a bouncy sort of' is the wordplay.
'a bouncy sort' becomes 'ech' (I am not sure about this - if you are sure you should believe this answer much more).
'of' becomes 'o''.
'ech'+'o'='ECHO'
Can you help me to learn more?
(Other definitions for echo that I've seen before include "Evocation" , "One who slavishly copies" , "She loved Narcissus - it's recalled" , "one catches on the rebound?" , "Nymph; E (radio comms.)" .)