cipher

also cy·pher (sīˈfər)

1. The mathematical symbol (0) denoting absence of quantity; zero.
2. An Arabic numeral or figure; a number.
3. One having no influence or value; a nonentity.
4. a. A cryptographic system in which units of plain text of regular length, usually letters, are arbitrarily transposed or substituted according to a predetermined code.
   b. The key to such a system.
   c. A message written or transmitted in such a system.
5. A design combining or interweaving letters or initials; a monogram.

1. To put in secret writing; encode.
2. To solve by means of arithmetic.