major third

major third (plural major thirds)

1. (music) A musical interval in Western music that is equal to or approximates a frequency ratio of 5/4. In twelve-tone equal temperament, it consists of four standard semitones, spans three degrees of the diatonic scale, and is enharmonically equivalent to a diminished fourth. Major scales are so named because of the major third interval between the tonic and mediant of a major tonic triad.

• M3