X-rated literature (4)
I believe the answer is:
smut
'x-rated literature' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for smut that I've seen before include "Soot flake or sexual innuendo" , "Mild obscenity" , "Bit of soot or dirty talk" , "Cereal disease; filth" , "blue material" .)