unisonous

This is from your frontispiece: Plainsong -- the unisonous vocal music used in the Christian church from the earliest times; any simple and unadorned melody or air.

Kent Haruf discusses Plainsong 2010

Yet even about the fourteenth century the gradual substitution of musica mensurata for the cantilena romana, part-music for unisonous, wrought an increasing change in the relation of choir to altar.

The Catholic Encyclopedia, Volume 3: Brownson-Clairvaux 1840-1916 1913

Superseding the primitive unisonous plain-song, the old parallel concords, and the simple faburden (faux bourdon) counterpoint that succeeded Gregory, they taught how musical tones can better assist worship with the beauty of harmony and the precision of scientific taste.

The Story of the Hymns and Tunes Theron Brown 1873

"Most owners are just wasting time in meetings with their insurance subscribers and so called Risk Management Companies, who often charge them an amount similar to the ransom demanded, while in most cases and at the end straight, fast and direct negotiations get the wanted result - the unharmed release of crew, ship and cargo," one regional analyst remarked and added: "The syndicate of so called professional negotiators work unisonous with the pirates and service companies, like tug-boat rentals for the cash-delivery and even governmental armed forces details, who all try to profit from the vice, but also ensure that nothing comes into the way of their business."

American Chronicle 2008