Meaning of “nullify” - Learner’s Dictionary

nullify

verb [ T ] uk us /ˈnʌlɪfaɪ/ formal
LOSE EFFECT

to make something lose its effect:

Advances in medicine have nullified the disease's effect.
LEGAL

to say officially that something has no legal power:

The judge could nullify the entire trial.

(Definition of “nullify” from the Cambridge Learner’s Dictionary © Cambridge University Press)