Source : Webster's Revised Unabridged Dictionary (1913)

Mes- \Mes-\
   See {Meso-}.

Meso- \Mes"o-\, Mes- \Mes-\ [Gr. me`sos in the middle.]
   A combining form denoting in the middle, intermediate;
   specif. (Chem.), denoting a type of hydrocarbons which are
   regarded as methenyl derivatives. Also used adjectively.