The greater septimal tritone is the musical interval corresponding to the 10:7 ratio in the harmonic series, and the inversion of the lesser septimal tritone. It is only slightly larger than the 7:5 ratio, the septimal tritone. Because these two intervals are so similar in size, and because most western music, and Arab music as well, does not distinguish between the septimal tritone and its inversion, most listeners, including many trained musicians with a good ear, have the toughest time distinguishing between these two intervals, among any of the pairs of intervals of 31-ET.
The inverted septimal tritone implies a root a major third below the top note, or a septimal whole tone above the bottom note. Contrary to what the name suggests, the greater septimal tritone is harmonically weaker than the lesser septimal tritone.