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.

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.

• (chemistry) (of a molecule etc) consisting of three atoms
       Ozone is a triatomic form of oxygen