Get oysters with trifle (3)
I believe the answer is:
toy
'trifle' is the definition.
(I've seen this in another clue)
'get oysters with' is the wordplay.
'with' indicates a hidden word.
'TOY' is hidden in the letters of 'get oysters'.
(Other definitions for toy that I've seen before include "Child's amusement" , "Teddy or Dolly" , "A child's plaything" , "Object for a child to play with" , "One of spelt out words" .)