Indecent stuff (4)
I believe the answer is:
smut
'indecent stuff' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for smut that I've seen before include "Mild obscenity" , "Small flake of dirt" , "Pornography or grime" , "Dirty stuff" , "Cereal disease; filth" .)