A more thorough explanation:

Term: NEGATE
Definition:verb
1. To say that something is not true or does not exist.
2. To make something have no effect or value.
Examples:
1. The defendant's lawyer tried to negate the witness's testimony by proving that they had a history of lying.
2. Adding sugar to the recipe will negate the health benefits of the dish.
The first example shows how negating can be used to deny something. In this case, the lawyer is trying to prove that the witness is not telling the truth. The second example shows how negating can be used to nullify something. In this case, adding sugar to a healthy dish makes it less healthy.