Ditone

In music, a ditone (Latin: ditonus, from Ancient Greek: δίτονος, "of two tones") is the interval of a major third.

Because it is a comma wider than a "perfect" major third of 5:4, it is called a "comma-redundant" interval.

is more properly known as the Pythagorean ditone and consists of two major and two minor semitones (2M+2m).

The difference between the two systems is that Didymus places the minor tone below the major, whereas Ptolemy does the opposite.

[6] Modern writers occasionally use the word "ditone" to describe the interval of a major third in equal temperament.