antimatter

1. (physics) Matter that is composed of the antiparticles of those that constitute normal matter.Examples: "But most theories predict that equal amounts of matter and antimatter should have been produced during the big bang, and the mystery of what happened to all the antimatter is a central question in fundamental physics."uncountableusually

2. (physics) A form of matter that has a key property, such as charge, opposite to that of ordinary matter.Examples: "Particles of matter and antimatter are identical, except for an opposite electrical charge. An electron has a negative charge whereas its antiparticle, the positron, has a positive charge, and both have an identical mass."uncountableusually