If you are looking for Koichi, he is staring at an encyclopedia on the lounge chair in the sunroom.
The camera showed that you shoplifted an encyclopedia.
I used my encyclopedia as a pillow because it was too big to be a book.
Something filled with the rules of various actions is something that contains a ton of knowledge. It contains all things and actions, right? What kind of "thing" is filled with all this information (that existed during the creation of words and kanji?)? One thing would be an encyclopedia.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.