The Collaborative International Dictionary
Mes-
Mes- \Mes-\ See Meso-.
Mes-
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.
(Chem.) Optically inactive due to compensating optical activity at two or more asymmetric centers, often due to a plane of symmetry within the molecular structure; as, meso-tartaric acid.
Attached to a carbon atom located between two hereoatoms in a heterocyclic ring.
Wiktionary
mes-
pre. (form of prevocalic variant meso- English)