‖n. [ NL., fr. Gr. me`son middle, neut. of me`sos, a., middle. ] 1. (Anat.) The mesial plane dividing the body of an animal into similar right and left halves. The line in which it meets the dorsal surface has been called the dorsimeson, and the corresponding ventral edge the ventrimeson. B. G. Wilder. [ 1913 Webster ]

2. (Physics) An elementary particle made up of two quarks; a hadron having a baryon number of zero; any hadron other than a baryon. Mesons are bosons with integral values of spin, having a mass intermediate between those of the electron and a nucleon; they may have positive or negative charges, or may be neutral. Mesons are of three types: the pion (π-meson), kaon (K-mesons), and η-mesons. [ PJC ]

mu meson (Physics) the former name for the muon, a particle which is not a true meson{ 2 }. The term is no longer used in technical literature, except historically. [ PJC ]

a. [ Meso- + nasal. ] (Anat.) Of or pertaining to the middle portion of the nasal region. [ 1913 Webster ]

a. (Anat.) Of or pertaining to the mesonephros; as, the mesonephric, or Wolffian, duct. [ 1913 Webster ]

‖n. [ NL., fr. Gr. me`sos middle + nefro`s kidney. ] (Anat.) The middle one of the three pairs of embryonic renal organs developed in most vertebrates; the Wolffian body. [ 1913 Webster ]

a. Of or pertaining to a meson. [ PJC ]

‖n. [ NL., fr. Gr. me`sos middle + nw^ton the back. ] (Zool.) The dorsal portion of the mesothorax of insects. [ 1913 Webster ]