Dictionary.net

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.

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.

Containing three atoms, or three replaceable hydrogen atoms.

Of molecules of elementary bodies, containing three atoms.

Of compounds, containing three atoms of replaceable hydrogen.

Of radicles, having a combining capacity that is saturated by union with three hydrogen atoms. [Gr.].