diatonic

WordReference Random House Unabridged Dictionary of American English © 2015

di•a•ton•ic  (dī′ə ton′ik), 
adj. [Music.]

1. Chemistry, Music and Dance noting those scales that contain five whole tones and two semitones, as the major, minor, and certain modal scales.
2. Chemistry, Music and Dance of or pertaining to the tones, intervals, or harmonies of such scales.

Etymology:

• Greek diatonikós; see dia-, tonic
• Late Latin diatonicus
• 1590–1600

di′a•ton′i•cal•ly, adv. 

Collins Concise English Dictionary © HarperCollins Publishers::

diatonic /ˌdaɪəˈtɒnɪk/ adj

1. of, relating to, or based upon any scale of five tones and two semitones produced by playing the white keys of a keyboard instrument, esp the natural major or minor scales forming the basis of the key system in Western music
2. not involving the sharpening or flattening of the notes of the major or minor scale nor the use of such notes as modified by accidentals

Etymology: 16th Century: from Late Latin diatonicus, from Greek diatonikos, from diatonos extending, from diateinein to stretch out, from dia- + teinein to stretch