Sully, tarnish (5)
I believe the answer is:
taint
I believe this is a double definition.
'sully' is the first definition.
(I know that sully can be written as taint)
'tarnish' is the second definition.
(I've seen this before)
(Other definitions for taint that I've seen before include "contaminant" , "Contaminating influence" , "soil" , "Flaw in Titan" , "(Trace of) corruption" .)