The C-sharp half-diminished seventh chord (abbreviated "C#m7(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 minor seventh chord a half step.
C-sharp half-diminished seventh chord
C-sharp half-diminished chord C-sharp minor seventh flat five chord
C♯ E G B
1 ♭3 ♭5 ♭7
C♯ø C♯ø7 C♯m7b5 C♯–7(b5) C♯mi7(b5) C♯min7(b5)
Tetrad (four-note chord)