preemption in WordNet English dictionary

1. a prior appropriation of something
   "the preemption of bandwidth by commercial interests"
   preemption  pre-emption 
   
2. the right to purchase something in advance of others
   preemption  pre-emption 
   
3. the right of a government to seize or appropriate something (as property)
   preemption  pre-emption 
   
4. the judicial principle asserting the supremacy of federal over state legislation on the same subject
   preemption  pre-emption