diatonic (adj.)

c. 1600, in ancient Greek music, in reference to one of the three standard tetrachords, from French diatonique, from Latin diatonicus, from Greek diatonikos, from diatonos "extending; pertaining to the diatonic scale," from dia "through, across" (see dia-) + teinein "to stretch," from PIE root *ten- "to stretch." In modern music, "using tones, intervals, and harmonies of the standard major and minor scales without chromatic alteration," 1690s. Related: Diatonically.