hornbook

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An early primer consisting of a single page protected by a transparent sheet of horn, formerly used in teaching children to read.
• noun A text that instructs in the basic skills or rudiments of a subject.

from The Century Dictionary.

• noun A leaf or page, usually one containing the alphabet, the nine digits, and the Lord's Prayer, covered with transparent horn and fixed in a frame with a handle: formerly used in teaching children to read.
• noun Hence A book containing the first principles of any science or branch of knowledge; a primer.

from the GNU version of the Collaborative International Dictionary of English.

• noun The first book for children, or that from which in former times they learned their letters and rudiments; -- so called because a sheet of horn covered the small, thin board of oak, or the slip of paper, on which the alphabet, digits, and often the Lord's Prayer, were written or printed; a primer.
• noun A book containing the rudiments of any science or branch of knowledge; a manual; a handbook.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun law A legal textbook that gives a basic overview of a particular area of law.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a primer that provides instruction in the rudiments or basic skills of a branch of knowledge