Lewd material (4)
I believe the answer is:
smut
'lewd material' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for smut that I've seen before include "Soot, dirt, grit" , "Small bit of soot" , "Lewd material" , "Obscene word(s)" , "porn?" .)