Definition of "antiproton"
(physics) The antiparticle of the proton, having a negative electric charge.
Quotations
There were also particles no one had predicted that just appeared. Five of them […, i]n order of increasing modernity, […] are the neutrino, the pi meson, the antiproton, the quark and the Higgs boson.
2012 March-April, Jeremy Bernstein, “A Palette of Particles”, in American Scientist, volume 100, number 2, page 146