D defs.my
Entry 1 sense Webster, 1913

Plagal

/(plā"gal)/ · Pla·gal · IPA /ˈpleɪɡəl/
01 a. Having a scale running from the dominant to its octave; -- said of certain old church modes or tunes, as opposed to those called authentic,…
  1. 1.
    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.(Mus.)
Phrases & compounds
Plagal cadence — a cadence in which the final chord on the tonic is preceded by the chord on the subdominant.