Answer:
The best description of plainchant music is:
-Secular.
Step-by-step explanation:
The term plainchant (plain song) designates the traditional vocal music of the Christian liturgies, which is official of the Roman rite. This is essentially monodic, that is, it consists of a single melodic line, and is usually sung a capella. It is articulated by a free rhythm, which is essential according to any old treatise that deals with respect.