Speech only concealing sound reflection (4)
I believe the answer is:
echo
'sound reflection' is the definition.
('echo' can be a synonym of 'sound reflection')
'speech only concealing' is the wordplay.
'concealing' indicates the answer is hidden within the clue.
'ECHO' is hidden in the letters of 'speech only'.
(Other definitions for echo that I've seen before include "one catches on the rebound?" , "A natural sound reflection" , "from Brussels?" , "Ape" , "Nymph whose love Narcissus spurned" .)