\Tri`a*tom"ic\, a. [Pref. tri- + atomic.] (Chem.)
(a) Having three atoms; -- said of certain elements or
    radicals.
(b) Having a valence of three; trivalent; sometimes, in a
    specific sense, having three hydroxyl groups, whether
    acid or basic; thus, glycerin, glyceric acid, and
    tartronic acid are each triatomic.