Eleventh chord - Definition and Overview

In music or music theory an eleventh is the note eleven scale degrees from the root of chord and also the interval between the root and the eleventh.

An eleventh is a compound fourth.

An eleventh chord is a chord with an eleventh, and it is an extended chord if it includes the ninth. Added tone chords with what might be called an added eleventh are usually said to have an added fourth and are suspended chords.