ternary

Made up of three things.

Arranged in groups of three.

To the base three.

Perhaps the prettiest number system of all is the balanced ternary notation

Having three variables.

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.

Sodic hydroxide, NaOH, is a ternary compound.

A group of three things; a trio, threesome or tierce.

The Holy Trinity.

And albeit these thynges be waighty and truthes of great importance, yet (by the infinite goodnes of the Almighty Ternarie,) Artificiall Methods and easy wayes are made, by which the zelous Philosopher, may wyn nere this Riuerish Ida, this Mountayne of Contemplation […] .