Triad

Webster's Dictionary of the English Language

·noun A chord of three notes.

II. Triad ·noun An element or radical whose valence is three.

III. Triad ·noun The common chord, consisting of a tone with its third and fifth, with or without the octave.

IV. Triad ·noun A union of three; three objects treated as one; a ternary; a trinity; as, a triad of deities.