Why is the ninth month called September?
c.1200, "main division of a book," from Old French chapitre (12c.) "chapter (of a book), article (of a treaty), chapter (of a cathedral)," alteration of chapitle, from Late Latin capitulum, diminutive of caput (genitive capitis) "head" (see capitulum). Sense of "local branch" (1815) is from cathedral sense (late 15c.), which seems to trace to convocations of canons at cathedral churches, during which the rules of the order by chapter, or a chapter (capitulum) of Scripture, were read aloud to the assembled. Chapter and verse "in full and thoroughly" (1620s) is a reference to Scripture.
The several books of the Old and New Testaments were from an early time divided into chapters. The Pentateuch was divided by the ancient Hebrews into 54 _parshioth_ or sections, one of which was read in the synagogue every Sabbath day (Acts. 13:15). These sections were afterwards divided into 669 _sidrim_ or orders of unequal length. The Prophets were divided in somewhat the same manner into _haphtaroth_ or passages. In the early Latin and Greek versions of the Bible, similar divisions of the several books were made. The New Testament books were also divided into portions of various lengths under different names, such as titles and heads or chapters. In modern times this ancient example was imitated, and many attempts of the kind were made before the existing division into chapters was fixed. The Latin Bible published by Cardinal Hugo of St. Cher in A.D. 1240 is generally regarded as the first Bible that was divided into our present chapters, although it appears that some of the chapters were fixed as early as A.D. 1059. This division into chapters came gradually to be adopted in the published editions of the Hebrew, with some few variations, and of the Greek Scriptures, and hence of other versions.