In music theory, an eleventh chord is a chord that contains the tertian extension of the eleventh. Typically found in jazz, an eleventh chord also usually includes the seventh and ninth, and elements of the basic triad structure. Variants include the dominant eleventh (C, C–E–G–B♭–D–F), minor eleventh (Cm, C–E♭–G–B♭–D–F), and major eleventh chord (Cmaj, C–E–G–B–D–F). Using an augmented eleventh produces the dominant sharp eleventh (C, C–E–G–B♭–D–F♯) and major ninth sharp eleventh (Cmaj, C–E–G–B–D–F♯) chords.
A perfect eleventh creates a highly dissonant minor ninth interval with the major third of major and dominant chords. To reduce this dissonance the third is often omitted (such as for example in the dominant eleventh chord that can be heard 52 seconds into the song "Sun King" on The Beatles' Abbey Road album), turning the chord into a suspended ninth chord (e.g. C, C–G–B♭–D–F), which can be also notated as Gm/C.
