triad Meaning, Definition & Usage

  1. noun the cardinal number that is the sum of one and one and one
    deuce-ace; trio; triplet; tercet; tierce; troika; three; trey; 3; ternion; trine; ternary; threesome; leash; III; trinity; terzetto.
  2. noun a set of three similar things considered as a unit
    trio; triplet; triple.
  3. noun three people considered as a unit
    threesome; trio; trinity.
  4. noun a three-note major or minor chord; a note and its third and fifth tones
    common chord.

WordNet

Tri"ad noun
Etymology
L.trias, -adis, Gr. , , fr., , three: cf. F. triade. See Three, and cf. Trias, Trio.
Definitions
  1. A union of three; three objects treated as one; a ternary; a trinity; as, a triad of deities.
  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.
  3. (Chem.) An element or radical whose valence is three.

Webster 1913