pla·gal (plā'gəl) adj.
Music Of or being a medieval mode having a range from the fourth below to the fifth above its final tone.
[Medieval Latin plagālis, from plaga, plagal mode, from plagius, plagal, from Medieval Greek plagios (ēkhos), plagal (mode), from Greek, oblique, from plagos, side; see plāk-1 in Indo-European roots.]