A9 chord
The A dominant ninth chord (abbreviated "A9 chord") is a five-note chord consisting of the notes A, C♯, E, G, and B. The chord is formed by adding a major ninth to a A dominant seventh chord.
In practice, the fifth (E) is sometimes omitted from the A9 chord because it's not always possible to play all notes simultaneously.
Name
A dominant ninth chord
Notes
A C♯ E G B
Intervals
1 3 5 ♭7 9
Chord symbol
A9
Type
Pentad (five-note chord)