The Collaborative International Dictionary of English v.0.48:

mesotartaric \mes`o*tar*tar"ic\, a. [Meso- + tartaric.] (Chem.)
   Pertaining to, or designating, an acid called also inactive
   tartaric acid. It is an optically inactive stereoisomer of
   tartaric acid due to internal compensation of the rotatory
   activity of the two asymmetric centers; it has a plane of
   symmetry in the molecule.
   [1913 Webster +PJC]