1. 
   Plagal
   Pla'gal adjective [ French, from Greek ... 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 it...
   Found op http://www.encyclo.co.uk/webster/P/98
   
   
2. 
   Plagal
   • (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, which ran from the tonic to its octave.
   Found op http://thinkexist.com/dictionary/meaning/plagal/
   
   
3. 
   Plagal
   In music, plagal describes a piece as having a scale running from the dominant to its octave. It is said of certain old church modes or tunes, as opposed to those called authentic, which ran from the tonic to its octave.
   Found op http://www.probertencyclopaedia.com/browse/VP.HTM
   
   

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