Why is the ninth month called September?
1540s, "brief statement;" sense of "short prayer book used by Catholic priests" is from 1610s, from Latin breviarium "summary," noun use of neuter of adjective breviarius "abridged," from breviare "to shorten, abbreviate," from brevis "short" (see brief (adj.)).
liturgical book in the Roman Catholic Church that contains the daily service for the divine office, the official prayer of the church consisting of psalms, readings, and hymns that are recited at stated hours of the day. The breviary (Latin breviarium, "abridgment") as a condensed tome appeared only after the divine office itself was fixed and widely used and after the recitation of the office had come to be regarded as obligatory for individuals not residing in a community