preempt
verb[T]
us/priˈempt/topreventsomething fromhappeningby takingactionfirst:
Statelawspreemptedlocalgovernmentsfromrestrictingnewspaperdisplays.
If abroadcastis preempted, it isreplacedby another, usually moreimportantbroadcast:
OnestationpreempteditsFridaynightscheduletotelevisethe highschoolplayoffs.
preemptive
adjective[not gradable](alsopre-emptive)us/priˈemp·tɪv/
a preemptiveairstrikeon anenemybase