Source : Webster's Revised Unabridged Dictionary (1913)

Meson \Mes"on\, n. [NL., fr. Gr. me`son middle, neut. of me`sos,
   a., middle.] (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.

Source : WordNet®

meson
     n : an elementary particle responsible for the forces in the
         atomic nucleus; a hadron with a baryon number of 0 [syn:
         {mesotron}]