/ ˈnʌlɪfaɪ; NAmE / verb ( nul·li·fies , nul·li·fy·ing , nul·li·fied , nul·li·fied ) [ vn ] ( formal )
1.
to make sth such as an agreement or order lose its legal force
SYN invalidate :
Judges were unwilling to nullify government decisions.
2.
to make sth lose its effect or power
SYN negate :
An unhealthy diet will nullify the effects of training.