n. plural See the Triad Society.n. A union or conjunction of three; a group or class of three persons or things closely related; a trinity.n. In chem., an element or radical which will combine with three atoms of a monad element or radical; a trivalent element or radical.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.n. In Welsh lit., a form of composition characterized by the arrangement of the contents in groups of three.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.n. In morphology, a tertiary unit of organization resulting; from integration of an aggregate of dyads. See dyad, 3.n. An indeterminate product of three vectors.