Source : WordNet®

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