1. (a.) Having three atoms; -- said of certain elements or radicals.

2. (a.) 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.

a certain an any any one atomatic atomiferous atomistic corpuscular cyclic diatomic dibasic either embryonic evanescent exclusive germinal granular heteroatomic heterocyclic hexatomic homocyclic impalpable imperceptible imponderable inappreciable indiscernible individual indivisible infinitesimal intangible integral invisible irreducible isobaric isocyclic isoteric isotopic lone microcosmic microscopic molecular monadic monatomic monistic one pentatomic simple single singular sole solid solitary subatomic tenuous tetratomic thin triatomic tribasic ultramicroscopic unanalyzable undivided uniform unique unitary unseeable whole