to render (somebody else's action or intention) pointless or ineffective by acting first; to forestall (something)

The government's decision to build an airport preempted the council's plans

to take (something) over, esp to prevent others having it; to appropriate (something)

The movement was then preempted by a lunatic fringe

to acquire (something) by preemption

to take the place of (something)

to make a preemptive bid in bridge