What is the X in X-mas?
Old English boc "book, writing, written document," traditionally from Proto-Germanic *bokiz "beech" (cf. German Buch "book" Buche "beech;" see beech), the notion being of beechwood tablets on which runes were inscribed, but it may be from the tree itself (people still carve initials in them). The Old English word originally meant any written document. Latin and Sanskrit also have words for "writing" that are based on tree names ("birch" and "ash," respectively). Meaning "libretto of an opera" is from 1768. A betting book is from 1856.
Old English bocian "to grant or assign by charter," from book (n.). Meaning "to enter into a book, record" is early 13c. Meaning "to enter for a seat or place, issue (railway) tickets" is from 1841; "to engage a performer as a guest" is from 1872. Related: Booked; booking.
by the book, crack a book, hit the books, in someone's bad books, little black book, one for the book, pound the books, read someone like a book, stroke book, take a page from someone's book, throw the book at someone, wish book, write the book
This word has a comprehensive meaning in Scripture. In the Old Testament it is the rendering of the Hebrew word _sepher_, which properly means a "writing," and then a "volume" (Ex. 17:14; Deut. 28:58; 29:20; Job 19:23) or "roll of a book" (Jer. 36:2, 4). Books were originally written on skins, on linen or cotton cloth, and on Egyptian papyrus, whence our word "paper." The leaves of the book were generally written in columns, designated by a Hebrew word properly meaning "doors" and "valves" (Jer. 36:23, R.V., marg. "columns"). Among the Hebrews books were generally rolled up like our maps, or if very long they were rolled from both ends, forming two rolls (Luke 4:17-20). Thus they were arranged when the writing was on flexible materials; but if the writing was on tablets of wood or brass or lead, then the several tablets were bound together by rings through which a rod was passed. A sealed book is one whose contents are secret (Isa. 29:11; Rev. 5:1-3). To "eat" a book (Jer. 15:16; Ezek. 2:8-10; 3:1-3; Rev. 10:9) is to study its contents carefully. The book of judgment (Dan. 7:10) refers to the method of human courts of justice as illustrating the proceedings which will take place at the day of God's final judgment. The book of the wars of the Lord (Num. 21:14), the book of Jasher (Josh. 10:13), and the book of the chronicles of the kings of Judah and Israel (2 Chr. 25:26), were probably ancient documents known to the Hebrews, but not forming a part of the canon. The book of life (Ps. 69:28) suggests the idea that as the redeemed form a community or citizenship (Phil. 3:20; 4:3), a catalogue of the citizens' names is preserved (Luke 10:20; Rev. 20:15). Their names are registered in heaven (Luke 10:20; Rev. 3:5). The book of the covenant (Ex. 24:7), containing Ex. 20:22-23:33, is the first book actually mentioned as a part of the written word. It contains a series of laws, civil, social, and religious, given to Moses at Sinai immediately after the delivery of the decalogue. These were written in this "book."