Augmented seventh chord

[2] It can be viewed as an augmented triad with a minor seventh.

The root is the only optional note in an augmented seventh chord, the fifth being required because it is raised.

[4] This alteration is useful in the major mode because the raised 5th creates a leading tone to the 3rd of the tonic triad.

In rock parlance, the term augmented seventh chord is sometimes confusingly and erroneously used to refer to the so-called "Hendrix chord", a 7♯9 chord which contains the interval of an augmented ninth but not an augmented fifth.

Overall, however, the augmented seventh chord is infrequently used, often with the raised fifth degree being the result of a chromatic passing tone.