Dirty and depressed (4)
I believe the answer is:
blue
I believe this is a double definition.
'dirty' is the first definition.
(blue can mean pornographic)
'depressed' is the second definition.
(I've seen this before)
'and' acts as a link.
(Other definitions for blue that I've seen before include "Oxbridge sportsman; sad" , "Oxbridge player" , "Miserable - cerulean" , "Conservative > depressed" , "entertaining rabbi" .)