Grimoire

Grimoire is a book of witchcraft or paranormal magic. The word is pronounced "grim-warr", which rhymes with "guitar".
The word is a mistaken way of saying "grammar". It probably started being used in a time when not many people could read. Then any book might be thought to contain instructions for magic.
In the religion of Wicca and other forms of Neopaganism, such a book is sometimes called a "Book of Shadows".