Meson

Definitions

1. The mesial plane dividing the body into similar right and left halves.
   regional
2. A member of a group of subatomic particles having a mass intermediate between electrons and protons. (The most easily detected mesons fit this definition.)
   obsolete
3. 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.)
   particle, specifically

Equivalents

CEFR level