From CryptoDox, The Online Encyclopedia on Cryptography and Information Security
The word Cryptanalysis originated from the Greek kryptós; which means "hidden", and analýein, "to loosen" or "to untie"). It is the study of methods for obtaining the meaning of encrypted information, without access to the secret information which is normally required to do so. Typically, this involves finding the secret key. In non-technical language, this is the practice of codebreaking or cracking the code, although these phrases also have a specialised technical meaning.
History of Cryptanalysis
Methods of cryptanalysis