triad

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A group of three.
2. n. 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. n. A section of a Pindaric ode consisting of the strophe, antistrophe, and epode.

Century Dictionary and Cyclopedia

1. n. plural See the Triad Society.
2. n. A union or conjunction of three; a group or class of three persons or things closely related; a trinity.
3. n. In chem., an element or radical which will combine with three atoms of a monad element or radical; a trivalent element or radical.
4. n. In music, a chord of three tones, including a given tone with its major or minor third and its perfect, augmented, or diminished fifth. A triad is named from the given tone or root: as, triad of G; dominant triad. See chord, 4. Also trias.
5. n. In Welsh lit., a form of composition characterized by the arrangement of the contents in groups of three. The earliest specimens of these triads belong to the twelfth century. The method was continued for several centuries in Wales, but was not imitated elsewhere except in a few instances in Ireland.
6. n. In mythology, an intimate association of three kindred or correlated deities, sometimes considered as having the relationship of father, mother, and child, and forming a characteristic conception in some religious systems, as that of ancient Egypt.
7. n. In morphology, a tertiary unit of organization resulting; from integration of an aggregate of dyads. See dyad, 3.
8. n. An indeterminate product of three vectors.

Wiktionary

1. n. A grouping of three.
2. n. music A chord consisting of a root tone, the tone two degrees higher, and the tone four degrees higher in a given scale.
3. n. electronics on a CRT display, a group of three neighbouring phosphor dots, coloured green, red, and blue.
4. n. A branch of a Chinese underground criminal society, mostly based in Hong Kong.

GNU Webster's 1913

1. n. A union of three; three objects treated as one; a ternary; a trinity.
2. n. A chord of three notes.
3. n. The common chord, consisting of a tone with its third and fifth, with or without the octave.
4. n. (Chem.) An element or radical whose valence is three.

WordNet 3.0

1. n. three people considered as a unit
2. n. a three-note major or minor chord; a note and its third and fifth tones
3. n. a set of three similar things considered as a unit
4. n. the cardinal number that is the sum of one and one and one