Source : Webster's Revised Unabridged Dictionary (1913)

Trivalent \Triv"a*lent\, a. [Pref. tri- + L. valens, -entis, p.
   pr. See {Valence}.] (Chem.)
   Having a valence of three; capable of being combined with,
   substituted for, or compared with, three atoms of hydrogen;
   -- said of triad atoms or radicals; thus, nitrogen is
   trivalent in ammonia.

Source : WordNet®

trivalent
     adj : having a valence of three