Sentence:  Infants learned their letters from a <WSD>hornbook</WSD>, a square of wood shaped like a table-tennis bat on which were pasted the alphabet, syllables and the Lord's Prayer ... 
Meaning of the word marked with <WSD> tags:  A single page containing the alphabet, covered with a sheet of transparent horn, formerly used for teaching children to read.<ref name="ADPM-def">The '''[http://books.google.com/books?id=Z_QUAAAAIAAJ&pg=PA269&dq=hornbook++subject:%22Book+industries+and+trade%22&as_brr=3&ei=IFwqR7jTPI307QKDkYW-BQ American Dictionary of Printing and Bookmaking]''' by W.W. Pasko (1894)</ref>