The Collaborative International Dictionary of English v.0.48:

Trimellic \Tri*mel"lic\, a. [Pref. tri- + L. mel, gen. mellis,
   honey.] (Chem.)
   Of, pertaining to, or designating, a certain tribasic acid
   (called also trimellitic acid) metameric with trimesitic
   acid.
   [1913 Webster]