triadic

being or relating to a triad, or group of three, especially a group of three closely related people or things: Red and blue form two parts of a triadic color scheme that also includes yellow or a neutral color such as black, gray, or white.

Music. being or relating to a chord of three tones, especially one consisting of a particular tone with its major or minor third and its perfect, augmented, or diminished fifth: We can add to this progression by putting a triadic major chord at the beginning of each bar.