meson

noun

Etymology: From meso- + -on. Coined by Indian physicist Homi Bhabha in 1939, as a modification of the earlier suggestion mesotron.

1. A member of a group of subatomic particles having a mass intermediate between electrons and protons. (The most easily detected mesons fit this definition.)
2. An elementary particle that is composed of a quark and an antiquark, such as a kaon or pion. (Mesons composed of rarer quarks are much heavier.)