To destroy completely: The naval force was annihilated during the attack. To reduce to nonexistence:"He had not just to hide his hunger; so as not to go mad he had to annihilate it"(Philip Roth). To defeat decisively: annihilated the league champions in the playoffs. Physics To convert (a subatomic particle) to energy or high-energy particles by annihilation. To be completely destructive. Physics To participate in annihilation. Used of particles and antiparticles.