Triatomic
Triatomic , adjective
[Prefix tri- + atomic.]
(a)
(Chemistry) Having three atoms; -- said of certain elements or radicals.
(b)
(Chemistry) 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.