Notes proper to a key.
diatonic chord is one having no note chromatically altered.
diatonic harmony is formed by the tones of a single minor or major scale;
diatonic interval is formed by two tones of the major or minor scale. A diatonic interval is one formed of two notes of a diatonic scale unaltered by accidentals.
diatonic melody is one not including notes belonging to more than one scale.
diatonic modulation is one by which a key is changed to another closely related to it.
Diatonic Ninths - "On the diatonic ninths, atomic vibration reaches 900,000,000. On the Dominant Etheric Sixths, 8,100,000,000. On the Interetheric ninths, 24,300,000,000 all of which can be demonstrated by sound colors." [Keely and His Discoveries]
1) One of the three genera of music among the Greeks, the other two being the chromatic and enharmonic.
2) The modern major and minor scales.
3) Chords, intervals, and melodic progressions, etc., belonging to one key-scale. A diatonic chord is one having no note chromatically altered. A diatonic interval is one formed by two notes of a diatonic scale unaltered by accidentals.
4) The scale of eight tones, the 8th being the octave of the first. Other scales are major scale and minor scale, which are also classed as diatonic.
DOMINANT, DIATONIC THIRDS: "The fundamental mode of vibration changes as we reach the fifth subdivision, to the dominant, the diatonic third of the mass chord, which controls the vibratory states of both etheron and interetheron." [Keely and His Discoveries]