Plastic fish (3)
I believe the answer is:
cod
I believe this is a double definition.
'plastic' is the first definition.
(both can mean fake or inauthentic)
'fish' is the second definition.
(cod is a kind of fish)
(Other definitions for cod that I've seen before include "No payment in advance" , "swimmer" , "A fish; a hoax (slang)" , "A white fish" , "Tasty fish or slangy nonsense" .)