The word grimoire is from the Old French gramaire, and is from the same root as the words grammar and glamour. This is partly because, in the mid-late Middle Ages, Latin "grammars" (books on Latin syntax and diction) were foundational to school and university education, as controlled by the Church - while to the illiterate majority, non-ecclesiastical books were suspect as magic. But "grammar" also denoted, to literate and illiterate alike, a book of basic instruction. A grammar is a description of a set of symbols and how to combine them to create well-formed sentences. A Grimoire is, appropriately enough, a description of a set of magickal symbols and how to combine them properly.
Origin: asatru-religion.blogspot.com