Enneachord

But Aristoxenus calls the following foreign instruments — phœnices, and pectides, and magadides, and sambucæ, and triangles, and clepsiambi, and scindapsi, and the instrument called the enneachord or nine-stringed instrument.

Source: wiktionary

The heptatonic system above must be radically segregated from an older model described in UET VII, 74, where the generative paradigm comes from an instrument fitted with nine strings, the enneachord, exposing the theory of a nine note system that is called enneatonism.

Source: wiktionary

So Apollo's instrument, a sixteenth-century lira da braccio with nine strings like the Greek enneachord given over to the nine muses, serves as the culmination of the lyre's development, as pictured in the Parnassus by Raphael.

Source: wiktionary

For while we are used to simply dividing modes internally in terms of fifths and fourths to make an octave, Jacques complicates matters for us by introducing concepts from the monochord in Liber V, thus enneachords and decachords, i. e., ranges of nine and ten notes. […] The sixth tone forms an enneachord (C-d) and does not contain a diapente under its proper ending, but rather (again) a semitritone.

Source: wiktionary