The A half-diminished seventh chord (abbreviated "Am7(b5) chord") is a four-note chord consisting of the notes A, C, E♭, and G. The chord is formed by lowering the fifth of a A minor seventh chord a half step.
A half-diminished seventh chord
A half-diminished chord A minor seventh flat five chord
A C E♭ G
1 ♭3 ♭5 ♭7
Aø Aø7 Am7b5 A–7(b5) Ami7(b5) Amin7(b5)
Tetrad (four-note chord)