Adulterate (verb)

1. To make impure by adding inferior or tainted substances.
2. To reduce the purity or effectiveness of a substance by adding something else to it.

Origin:

From the latin word adulterāre, meaning "to corrupt, debase, or make impure".

Examples:

1. The company was accused of adulterating their products with cheap fillers.
2. The food inspector found that the milk had been adulterated with water.
3. The wine had been adulterated with cheaper grape juice.
4. The company adulterated the gasoline with kerosene.
5. The drugs had been adulterated with unknown substances.