Tainted (6)
I believe the answer is:
impure
'tainted' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for impure that I've seen before include "Assign a value to" , "Sullied or adulterated" , "Adulterated or unchaste" , "Tainted, not chaste" , "Contaminated or licentious" .)