Meson
Part of speech: noun
Definition: The mesial plane dividing the body into similar right and left halves. A member of a group of subatomic particles having a mass intermediate between electrons and protons. (The most easily detected mesons fit this definition.) An elementary particle that is composed of a quark and an antiquark, such as a kaon or pion. (Meson composed of rarer quarks are much heavier.)
Mesotron
Part of speech: noun
Definition: meson