Infamous marquis (2,4)
I believe the answer is:
de sade
'infamous marquis' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for de sade that I've seen before include "The Marquis . . . . . . is a byword for cruelty" , "Notorious French marquis, d. 1814" , "French author many considered depraved" .)