The Collaborative International Dictionary of English v.0.48:

Triad \Tri"ad\, n. [L. trias, -adis, Gr. ?, ?, fr.?, ?, 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.
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   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.
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   3. (Chem.) An element or radical whose valence is three.
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   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.
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