Silent type (4)
I believe the answer is:
clam
'silent type' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for clam that I've seen before include "Mollusc with firmly-closed shell" , "Bi-valve with firmly-closed shell" , "Mollusc with tightly-closed shell" , "A silent type" , "Large shellfish with hinged shell" .)