Chumash (also ?umash; Hebrew: ?, pronounced [?u'ma?] or pronounced [?u'ma?] or Yiddish: pronounced ['m]; plural ?umashim) is a Torah in printed form (i.e. codex) as opposed to a Sefer Torah, which is a scroll.
The word comes from the Hebrew word for five, ?amesh (). A more formal term is ?amishah ?umshei Torah, "five fifths of Torah". It is also known by the Latinised Greek term Pentateuch in common printed editions.
The word "?umash" may be a vowel alteration of ?omesh, meaning "one-fifth", alluding to any one of the five books: as the Hebrew ? has no vowel signs, it could be read either way. It could also be regarded as a back-formed singular of ?umashim/?umshei (which is, in fact, the plural of ?omesh).
In early scribal practice, there was a distinction between a Sefer Torah, containing the entire Pentateuch on a parchment scroll, and a copy of one of the five books on its own, which was generally bound in codex form, like a modern book, and had a lesser degree of sanctity. The term ?omesh strictly applies to one of the latter. Thus, ?omesh B'reshit strictly means "the Genesis fifth", but was misread as ?umash, B'reshit and interpreted as meaning "The Pentateuch: Genesis", as if "?umash" was the name of the book and "Bereshit" the name of one of its parts. Compare the misunderstanding of "Tur" to mean the entirety of the Arba'ah Turim.
In the legal codes, such as Maimonides' Mishneh Torah, it is laid down that any copy of the Pentateuch which does not comply with the strict rules for a Sefer Torah, for example, because it is not a parchment scroll or contains vowel signs, has only the same sanctity as a copy of an individual book (?omesh). In this way, the word ?omesh (or ?umash) came to have the extended sense of any copy of the Pentateuch other than a Sefer Torah.
The word ?umash generally only refers to "book" bound editions of the Pentateuch, whereas the "scroll" form is called a sefer Torah ("book [of the] Torah").
In modern Jewish practice: