A cylinder whose lettered rings must be turned to spell the word that opens it. A coined word, crypt + codex. The container and the password are one object: the answer is not kept inside the lock, the answer IS the lock.
Modern coinage from crypt (Greek κρυπτός, kryptos, hidden) + codex (Latin, a bound book); a cylinder whose lettered rings must be turned to spell the word that opens it, made so the answer and the lock are one object.
A cylinder whose rings must be turned to spell the word that opens it. The answer is never hidden inside the lock — the answer is the lock.