Hornbook

Webster's Dictionary

(1): (n.) 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.

(2): (n.) A book containing the rudiments of any science or branch of knowledge; a manual; a handbook.

The Nuttall Encyclopedia

Was a sheet of vellum or paper used in early times for teaching the rudiments of education, on which were inscribed the alphabet in black or Roman letters, some monosyllables, the Lord's Prayer, and the Roman numerals; this sheet was covered with a slice of transparent horn, and was still in use in George II.'s reign.