Merriam-Webster Collegiate Dictionary - preemptive

 adjective  Date: 1855  1.  a. of or relating to preemption  b. having power to preempt  2. of a bid in bridge higher than necessary and intended to shut out bids by the opponents  3. giving a stockholder first option to purchase new stock in an amount proportionate to his existing holdings  4. marked by the seizing of the initiative ; initiated by oneself a ~ attack  • ~ly adverb