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' says the answer is hidden in 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" .)