The third above the keynote; -- so called because it divides the interval between the tonic and dominant into two thirds.

the note or chord on the third degree of the major scale. Often marked with the Roman numeral III.

(music) the third note of a diatonic scale; midway between the tonic and the dominant

The third tone of a scale.

The third scale degree in the Western major or minor scales.

The third degree of the major or minor scale. The triad built on this degree is labeled iii in the major scale, III in the natural minor scale, and III+ in the harmonic minor scale.