major third

major third (plural major thirds)

1. (music) A musical interval of the Western twelve-semitone system consisting of four semitones and spanning three degrees of the diatonic scale. Major scales are so named because of the major third interval between the tonic and mediant of a major tonic triad. It is enharmonically equivalent to a diminished fourth.

   The major third has a pitch ratio close to 34:27.

• M3