Playable, correctly spelled, and not how the chord is normally voiced. Right now this is the shapes that put a ninth, eleventh or thirteenth below the root.
Ab9 is Ab, C, Eb, Gb and Bb — Ab7 with the ninth stacked on top.
It sounds bright and full, still clearly pulling. The ninth adds height without softening the tritone underneath it, which is why funk and soul comp on this rather than on a plain 7.
Dominant — the same pull as a 7, with more colour.

| Ab | C | Eb | Gb | Bb |
|---|---|---|---|---|
| 1 | 3 | 5 | ♭7 | 9 |
Also written Abdom9 or Ab dominant 9. The same chord either way; which spelling you meet depends on who wrote the chart.
Five notes and four fingers, so something has to go. Keep C and Gb (they fix the quality) and Bb (what the symbol is about). Let Eb and Ab go, in that order — a perfect fifth says nothing the root has not, and in a band the bass has the root.
Play Ab9 as a shell — root, third and seventh — and the spare string takes the #11 (D), the b13 (Fb) or the 13 (F).
All 8 common shapes as fret numbers, lowest string first. Hover or tap one to see it drawn.
Ab9 is the V of Db, and that is where it goes if it goes anywhere: the third and the flat seventh are a tritone apart, and both resolve by a semitone into Db.
In which keys. Every note of Ab9 belongs to C# major (the V, the dominant) and Bb minor (the ♭VII).
Every note of Ab9 is in Ab mixolydian and Ab lydian dominant.
Each of those is a page: the scale across the neck, and the chords it harmonises into — which is where Ab9 sits in it. Every scale.
Change one note of Ab9 and you have Abmaj9 (the flat seventh becomes the major seventh), Abm9 (the major third becomes the minor third), Abadd9 (drop the flat seventh), Ab69 (the flat seventh becomes the sixth), Ab7 (drop the ninth) or Ab9b5 (the fifth becomes the flat fifth).
Ab9 is a dominant chord — root, major third, fifth, minor seventh. Dominant seventh chords on every root.
The common shapes and the derived voicings come from different places, and both are explained in how this site is built.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.