Real Dictionary

diatonic in American English
designating, of, or using a scale of eight tones that is either a major scale or a , minor scale
adjective: noting those scales that contain five whole tones and two semitones, as the major, minor, and certain modal scales

diatonic in British English
adjective: 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