We have already noted in our introduction to the book of Genesis that the European names of the books of the Torah (Genesis, Exodus, Leviticus, Numbers, and Deuteronomy) are Jewish in origin. In ancient times each book of the Torah had two names, one based on the primary theme of the book, and the other taken from the book’s opening words. The first of those (rendered first into Greek and Latin, and from them into other languages) became the norm in European culture, while the other is consistently used in Jewish terminology.
The second book of the Torah was in antiquity called Sefer Yetzi’at Mizrayim (“The Book of the Exodus from Egypt”), later translated and shortened as, simply, “Exodus.”
Leviticus, the third book of the Torah, was called Torat Ha-Kohanim (“The Law of the Priesthood”), but the European translation replaced the Priests with the Levites as the more general term, hence “Leviticus.”
The fourth book was known in antiquity as Chumash Ha-Pekudim, “the Book of the Census,” which in the European tradition became “Numbers.”
The fifth book of the Torah was called Mishneh Torah, or literally, “The Repetition of the Torah”, which then became “Deuteronomy,” from the Greek, meaning “Second Law.”
But the European name of the Torah’s first book strayed furthest from the original. Sefer Ha-Yesharim, “The Book of the Upright” (i.e., the Patriarchs), became known as “Genesis, from the Greek word meaning “Birth,” or “Beginning.”
Finally, we note that the five books of the Torah are commonly known in European tradition as the Pentateuch, the Greek equivalent of “five books.”
The modern Hebrew names of the books of the Torah (Bereshit, Shemot, etc.) are taken from the names of the first weekly portion of each book (the weekly portions are named after one of their first few words). To avoid confusion, in this commentary we refer to the books using their European names (Genesis, Exodus, etc.), while leaving the Hebrew equivalent terms to refer to their opening weekly portions.
 The Hebrew term chumash (from chamesh, “five”) is used to refer either to the Five Books of the Torah collectively, or to any one of the five books individually.