ˈ ̷ ̷ˌ ̷ ̷ noun
1. : a child's primer formerly in use consisting typically of a sheet of parchment or later of paper mounted on a thin wooden board and protected by a sheet of transparent horn and having on it the alphabet and other rudiments such as the digits and often the Lord's Prayer — compare battledore 3
2. : a rudimentary treatise
hornbooks of political theory — V.O.Key