proceeding by threes; consisting of three; as, the ternary number was anciently esteemed a symbol of perfection, and held in great veneration.-containing, or consisting of, three different parts, as elements, atoms, groups, or radicals, which are regarded as having different functions or relations in the molecule; thus, sodic hydroxide, naoh, is a ternary compound.-a ternion; the number three; three things taken together; a triad.