Treated as plural: miscellaneous remarks and observations; notes, miscellanea. With singular concord: a book consisting of these, a commonplace book.
((n. pl.) A miscellaneous collection of notes, remarks, or
selections; a commonplace book; also, commentaries or notes.)
Origin:
Late 16th century. From classical Latin adversāria things written on one side of the page, notes, observations (Cicero), in post-classical Latin also commonplace book, use as noun (short for scripta adversāria) of neuter plural of adversārius.