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

PRE-EMPTION is a 11 letter word that starts with P.