C#11 chord

The C-sharp dominant eleventh chord (abbreviated C#11 chord) is a six-note chord consisting of the notes C♯, E♯, G♯, B, D♯, and F♯. The chord is formed by adding an eleventh to the C-sharp dominant ninth chord.

In practice, the third (E♯) and fifth (G♯) are often omitted from the C#11 chord to avoid a very dissonant sound, and because it's not always possible to play all notes simultaneously.