What does the word cipher mean?

Usage examples for cipher

  1. I asked him for cipher mail." – The Law-Breakers by Ridgwell Cullum
  2. I got out the cipher, and once more Genevieve and I put our heads together over it. – The Paternoster Ruby by Charles Edmonds Walk
  3. These fellows can't read a cipher. – Helmet of Navarre by Bertha Runkle