A dominant ninth is a dominant chord with a ninth, but that’s not what a major ninth chord is. The major ninth chord (or just ninth chord), as an extended chord, typically includes the seventh and ninth along with the basic triad structure. Thus, a Cmaj9 consists of C E G B and D . When the symbol “9” is not preceded by the word “major” or “maj”, the implied seventh is a dominant seventh—e.g. a C9 consists of C E G B♭ and D.