*plagal*

a. [ F., from Gr. pla`gios sidewise, slanting. ] (Mus.) Having a scale running from the dominant to its octave; -- said of certain old church modes or tunes, as opposed to those called authentic, which ran from the tonic to its octave. [ 1913 Webster ]

Plagal cadence, a cadence in which the final chord on the tonic is preceded by the chord on the subdominant. [ 1913 Webster ]