tetrardus

tetrardus [cf. τέταρτος], (mus.) fourth pair of psalm-tones (consisting of the seventh and eighth psalm-tones). autentus ~us ‥ plaga ~i Trop. Wint. 64; septimus tonus, sc. authentus ~us Odington 120; nec mirum videatur quod deuterus dicitur phrygius cum plaga ~i sic [l. sit] gravior, quia plaga tetrardiem [l. tetrardi est] pars acutissimi modi Ib. 126.