from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A book that lists the symbols of a code and their meanings.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A book, table, database, or other object that stores the mapping between plaintext words or phrases and their equivalents in a code.
- n. A lookup table.
code + book. (Wiktionary)