A group of three things; a trio, threesome or tierce.
The Holy Trinity.
Made up of three things; treble, triadic, triple, triplex.
Arranged in groups of three.
To the base three.
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.