Source : Webster's Revised Unabridged Dictionary (1913)

Triverbial \Tri*ver"bi*al\, a. [Pref. tri- + L. verbum a word.]
   (Rom. Antiq.)
   Pertaining to, or designating, certain days allowed to the
   pretor for hearing causes, when be might speak the three
   characteristic words of his office, do, dico, addico. They
   were called dies fasti.