\Pla"gal\, a. [F., from Gr. ? 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.
{Plagal cadence}, a cadence in which the final chord on the
   tonic is preceded by the chord on the subdominant.