antiparticle

Etymology

anti- + particle

noun

1. (physics) A subatomic particle corresponding to another particle with the same mass, spin and mean lifetime but with charge, parity, strangeness and other quantum numbers flipped in sign; a particle that has a reversed world line to another.
   There could be whole antiworlds and antipeople made out of antiparticles. However, if you meet your antiself, don't shake hands! 1988, Stephen Hawking, A Brief History of Time: From the Big Bang to Black Holes, page 75