The Collaborative International Dictionary of English v.0.48:

Triacid \Tri*ac"id\, a. [Pref. tri- + acid.] (Chem.)
   Capable of neutralizing three molecules of a monobasic acid
   or the equivalent; having three hydrogen atoms which may be
   acid radicals; -- said of certain bases; thus, glycerin is a
   triacid base.
   [1913 Webster]