-triad-

n. [ L. trias, -adis, Gr. &unr_;, &unr_;, fr.&unr_;, &unr_;, three: cf. F. triade. See Three, and cf. Trias, Trio. ] 1. A union of three; three objects treated as one; a ternary; a trinity; as, a triad of deities. [ 1913 Webster ]

2. (Mus.) (a) A chord of three notes. (b) The common chord, consisting of a tone with its third and fifth, with or without the octave. [ 1913 Webster ]

3. (Chem.) An element or radical whose valence is three. [ 1913 Webster ]

Triads of the Welsh bards, poetical histories, in which the facts recorded are grouped by threes, three things or circumstances of a kind being mentioned together. --
Hindu triad. See Trimurti. [ 1913 Webster ]