--noun (singular: cipher; plural: ciphers)

1. cypher: a message written in a secret code.
2. 0: a mathematical element that when added to another number yields the same number.
3. aught: a quantity of no importance.
4. cypher: a person of no influence.
5. cryptograph: a secret method of writing.

--verb (verb: cipher; 3rd person present: ciphers; past tense: ciphered; past participle: ciphered; gerund or present participle: ciphering)

6. to convert ordinary language into code.
7. to make a mathematical calculation or computation.
1399, from Middle Latin cifra, from Ar. sifr "zero", literature "empty, nothing", from safara "to be empty", loan-transl. of Skt. sunya-s "empty." Came to Europe with Arabic numerals. Original meaning "zero", then "any numeral", then (first in Fr. and It.) "coded message" (first attested in Eng. 1528), since early codes often substituted numbers for letters. The verb meaning "to do arithmetic (with Arabic numerals) first attested 1530.

In cryptography, a cipher is an algorithm for performing encryption or decryption—a series of well-defined steps that can be followed as a procedure. An alternative, less common term is encipherment. To encipher or encode is to convert information into cipher or code.