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 the answer is hidden within the clue.
'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" .)