Some of Savoy's terrific shellfish (6)
I believe the answer is:
oyster
'shellfish' is the definition.
(I know that oyster is a type of shellfish)
'some of savoy's terrific' is the wordplay.
'some of' indicates a hidden word.
'OYSTER' can be found hidden inside 'savoys terrific'.
(Other definitions for oyster that I've seen before include "Succulent bivalve swallowed quickly" , "Content of stew" , "Pearl-generating bivalve" , "Pearl-making mollusc" , "Pearl-yielding shellfish" .)