diatonic
🇺🇸
/ˌdaɪəˈtɑːnɪk/
🇬🇧
/ˌdaɪəˈtɒnɪk/
relating to or using the seven notes of a major or minor scale without any sharps or flats
The piece was composed in a purely diatonic style, which made it sound very traditional.