Source : Webster's Revised Unabridged Dictionary (1913)

Trimesitic \Tri`me*sit"ic\, a. [Pref. tri- + mesitylene + -ic.]
   (Chem.)
   Of, pertaining to, or designating, a tribasic acid,
   {C6H3.(CO2)3}, of the aromatic series, obtained, by the
   oxidation of mesitylene, as a white crystalline substance.
   [Written also {trimesic}.]