Get oysters with trifles (4)
I believe the answer is:
toys
'trifles' is the definition.
(I've seen this before)
'get oysters with' is the wordplay.
'with' indicates a hidden word.
'TOYS' is hidden within 'get oysters'.
(Other definitions for toys that I've seen before include "Small dogs" , "Children's playthings" , "Things that provide amusement" , "Fiddles" , "Chihuahuas?" .)