In music theory, a diminished major seventh chord is a seventh chord composed of a diminished triad and a major seventh.Jamini, Deborah. (2005). Harmony And Composition: Basics to Intermediate, p.204. . Thus, it is composed of a root note, together with a minor third, a diminished fifth, and a major seventh above the root: (1, 3, 5, 7). For example, the diminished major seventh chord built on C, commonly written as CoM7, has pitches C–E–G–B:
