ADULTERATE

to reduce purity by combining with inferior ingredients

SYN - debase, dilute, load, stretch

"It only took one small touch of Jimmy's finger to adulterate the homemade brew that had been prepared."

"Unlike the delicious organic vegetables they had had the night before, these vegetables had been adulterated many times over by chemicals, preservatives and substitutes."

"The group was in an interesting position, to accept any more new applicants would adulterate their scholastic work, but to continue to deny applicants would prevent them from acheiving their goals of expansion."