Particle Physics any of four short-lived mesons that are positive, negative, or neutral and have a mass of 495 MeV/c (about 970 times that of an electron)
Ka (the letter K) + (mes)on
See kaon in American Heritage Dictionary 4
noun Abbr. K
Any of a subgroup of unstable mesons that consist of an electrically charged form with a mass 966 times that of an electron and a neutral form with a mass 974 times that of an electron, produced as a result of a high-energy particle collision. Also called K-meson. See Table at subatomic particle.