tri·ad (trīăd′, -əd)
1. A group of three.
2. Music A chord of three tones, especially one built on a given root tone plus a major or minor third and a perfect fifth.
3. A section of a Pindaric ode consisting of the strophe, antistrophe, and epode.
[Late Latin trias, triad-, from Greek, the number three; see trei- in the Appendix of Indo-European roots.]
tri·adic (trī-ădĭk) adj.
(click for a larger image)triad
left to right: C major, E minor, and D diminished triads
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