Ci·pher n.
 1. Arith. A character [0] which, standing by itself, expresses nothing, but when placed at the right hand of a whole number, increases its value tenfold.
 2. One who, or that which, has no weight or influence.
    Here he was a mere cipher.   --W. Irving.
 3. A character in general, as a figure or letter. [Obs.]
    This wisdom began to be written in ciphers and characters and letters bearing the forms of creatures.   --Sir W. Raleigh.
 4. A combination or interweaving of letters, as the initials of a name; a device; a monogram; as, a painter's cipher, an engraver's cipher, etc.  The cut represents the initials N. W.
 5. A private alphabet, system of characters, or other mode of writing, contrived for the safe transmission of secrets; also, a writing in such characters.
    His father . . . engaged him when he was very young to write all his letters to England in cipher.   --Bp. Burnet.
 Cipher key, a key to assist in reading writings in cipher.