kaon

Any of a group of four mesons, one positively charged and one negatively charged, having a mass 966 times that of an electron, and two electrically neutral, having a mass 974 times that of an electron. The two charged kaons have the same mean lifetime, about 1.24 × 10⁻¹⁰ second; the two neutral kaons have lifetimes of about 9 × 10⁻¹¹ second and 5 × 10⁻⁸ second.

any of four unstable subatomic particles, mesons, they are a combination of a strange quark or antiquark and either an up or down quark or antiquark

an unstable meson produced as the result of a high-energy particle collision