forestaller

noun4

1. •
   Agent noun of forestall: one who, or that which, forestalls.
2. •
   (historical) One who preemptively purchases goods in order to drive up their market price for resale.
3. •
   (historical) A device that overrides an automatic brake signal.
4. •
   (no longer used) One who obstructs a road, especially in order to intercept traffic.