Taint, sully (8)
I believe the answer is:
besmirch
I believe this is a double definition.
'taint' is the first definition.
(thesaurus)
'sully' is the second definition.
(I know that sully can be written as besmirch)
(Other definitions for besmirch that I've seen before include "Foul" , "Damage (a reputation)" , "run down" , "soil" , "Sully" .)