(a) Prefixed to the names of musical modes in hypo-aeolian, hypodorian, hypo-ionian, hypolydian, hypomixolydian, hypophrygian, to denote either (a) the grave modes in Ancient Greek music, beginning at a definite interval below the ordinary Aeolian, Dorian, etc., or(b) the ‘plagal’ modes in medieval music, each of which has a compass a fourth below that of the corresponding ‘authentic’ mode.