polyalphabetic substitution

[pol-ee-al-fuh-bet-ik, pol-ee-]
noun Cryptography.
  1. a system of substitution that mixes together a number of cipher alphabets in a cryptogram so that each plaintext letter is represented by a cipher that repeatedly changes.

Origin of polyalphabetic substitution

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