A Dictionary of Music and Musicians/Hyper-
HYPER- (Gr. ὑπερ, over, above; Lat. super). A prefix, extensively used in the terminology of antient Greek music—wherein it appears in the names of the five Acute Modes—and thence transferred to the musical system of the Middle Ages. The nomenclature of the one system must, however, be very carefully distinguished from that of the other; for, though the same terms are, in many cases, common to both, they are used to designate very different things. For instance, the discarded Locrian Mode (B, C, D, E, F, G, A, B) is often called the Hyper-æolian, in recognition of the fact that its range lies a tone above that of the true Æolian; but this Mode has no connexion whatever with the Hyper-æolian of the Greeks; neither have the Authentic Modes, as we now use them, the slightest affinity with the Greek acute forms, though the prefix 'hyper' has sometimes been very unnecessarily added to the names of all of them. [See Modes.]
Greek authors constantly use the prepositions ὑπερ and ὑπο in what we should now consider an inverted sense; applying the former to grave sounds, and the latter to acute ones. This apparent contradiction vanishes when we remember that they are speaking, not of the gravity or acuteness of the sounds, but of the position on the lyre of the strings designed to produce them.
The prefix Hypo- (Gr. ὑπο, under, below; Lat. sub) was applied, in antient Greek music, to the names of the five Grave Modes. In the Middle Ages it was added to the names of the seven Plagal Modes—the Hypo-dorian, the Hypo-phrygian, the Hypo-lydian, the Hypo-mixo-lydian, the Hypo-æolian, the discarded Hypo-locrian, and the Hypo-ionian—the range of which lies a fourth below that of their Authentic originals. [See Modes.]
Early writers also add this prefix to the names of certain intervals, when reckoned downwards, instead of upwards; as Hypo-diatessaron ( = Subdiatessaron), a fourth below; Hypo-diapente ( = Subdiapente), a fifth below. [See Interval.]