Answer: adulterate

AnswerCrossword Clue
ADULTERATEMake impure
ADULTERATEDebase
ADULTERATEWater down, perhaps
ADULTERATEDebase by admixture.
ADULTERATEContaminate
ADULTERATECorrupt
adulterateto make impure by the addition of a foreign substance
adulterateRender (something) poorer in quality by adding another substance, typically an inferior one