Printing libellous piece that's plausible (4)
I believe the answer is:
glib
'plausible' is the definition.
(similar in meaning)
'printing libellous piece' is the wordplay.
'piece' says the answer is hidden in the clue.
'GLIB' is hidden within 'printing libellous'.
'that's' acts as a link.
(Other definitions for glib that I've seen before include "Bush" , "Insincerely fluent" , "Smooth-talking" , "slick in speech" , "Insincere, shallow" .)