The C-sharp dominant seventh flat five chord (abbreviated "C#7(b5) chord") is a four-note chord consisting of the notes C♯, E♯, G, and B. The chord is formed by lowering the fifth of a C-sharp dominant seventh chord a half step.
C-sharp dominant seventh flat five chord
C♯ E♯ G B
1 3 ♭5 ♭7
tetrad (four-note chord)