Some crass, lurid aspersion (4)
I believe the answer is:
slur
'aspersion' is the definition.
(I know that aspersion can be written as slur)
'some crass lurid' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'SLUR' can be found hidden inside 'crass lurid'.
(Other definitions for slur that I've seen before include "become inarticulate" , "Slight - mumble" , "Musical sign: "Run together"" , "Contentious allegation" , "Slight; blur" .)