monoalphabetic substitution

[mon-oh-al-fuh-bet-ik, mon-oh-]
noun Cryptography.
  1. a system of substitution that uses only one cipher alphabet in a cryptogram so that each plaintext letter is always represented by the same cipher.

Origin of monoalphabetic substitution

1935–40; mono- + alphabetic Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018