Adulterate – To make something weaker or of worse quality by adding another substance
You must be an adult to rate (adulterate) the purity of beer. It's checked in case another substance has been added to make it weaker or of worse quality.
Examples of adulterate in a sentence
They had to adulterate the food to increase the quantity.
To lower the concentration of the cleaning products, adulterate them with water.
These businesses didn't adulterate products by for example; putting leaves in tea or chalk in flour.