meson

Etymology 1

From Ancient Greek μέσον (méson, “middle”).

noun

1. (rare outside entomology) The mesial plane dividing the body into similar right and left halves.

Etymology 2

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

noun

1. (obsolete) 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. (now specifically, physics) 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.)