plagal
Concise Oxford English Dictionary © 2008 Oxford University Press:
plagal /ˈpleɪg(ə)l/
▶adjective Music (of a church mode) containing notes between the dominant and the note an octave higher. Compare with authentic.
– origin C16: from med. L. plagalis, from plaga ‘plagal mode’, from L. plagius, from Gk plagos ‘side’.
'plagal' also found in these Oxford entries:

