Make impure (11)
'make impure' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for adulterate that I've seen before include "Make poorer by adding another substance" , "Corrupt" , "add inferior material?" , "Contaminate" , "Reduce purity" .)
'make impure' is the definition.
(synonyms)
This is all the clue.
(Other definitions for contaminate that I've seen before include "Add impurities to" , "Make (something) impure" , "Taint" , "Add impurity to (something)" , "Poison" .)