antimatter

noun

1. (uncountable, usually)Matter that is composed of the antiparticles of those that constitute normal matter.

   “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.”

2. (uncountable, usually)A form of matter that has a key property, such as charge, opposite to that of ordinary matter.

   “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.”