I've always understood the origination of the term as follows -- and I could be wrong, but this is what I heard long ago --
There was a time, as we all know, where witches could've been anything from the local crone who also was good with herbal healing, to the young woman who would give great advice passed down in her family in regards to certain objects, gems, herbs etc... to help another family out of tough times. He could've been one of the first to discover how to turn herbal properties into actual medicine, but accused for brewing poisons. He could've just raised his family with the religion that his parents taught him from generations and generations back.
But times were changing. A new religion was sweeping through what people barely understood to be an empire. It wasn't just a village, or a city or a country anymore. It was part of a whole, and the ruler wanted things to be as one across all of his lands. There was a time when these ordinary and otherwise generally helpful people were called witches for the first time with malice. There had to be a certain conformity, and if there wasn't -- they would come. Those Others who worked for the ruler. They would come and tear apart a life for the sake of making that life exactly the same as everyone else. So those people who were now called Witches with malice in the voices of the Others had to write down their secrets to keep them. No longer could they be spoken out. No longer could neighbors sit in their yard and ask for help where others might hear them. No longer could mothers pass down their knowledge to their daughters by practice alone. All had to be secret until the Others passed through, left forever and their uniform society was achieved.
So they wrote -- those who were able to. They wrote their secrets in little books, unassuming and average in appearance. And when they wrote their secrets in such a book, they would place it in the shadows of their homes -- in the darkest corners that would, with any luck, be overlooked if one of the Others would come searching. And when it was time for them to pass down their secrets, they removed their book from the shadows and handed it down to the next. And so these books filled with secrets became known as books of shadow, and were not spoken of except among those who would be called Witches with malice in the voices of those who spoke the word. And only then the book of shadows would only be discussed in the shadow of night under the light of the moon.
(This particular retelling of the story copyright to K.M. Alleena)
There's a certain mystery to the terminology, "Book of Shadows," I'll admit. As discussed in a recent post, words like "dark," "black," and "shadow" tend to get negative connotation when spoken of in terms of paganism and witchcraft. But certainly it's not always that way.
If you could rename the book of shadows, would you? Why? Why not? And what would you call it, theoretically speaking?