Definitions for "Substitution cipher"
A system of encryption in which each letter of a message is replaced with another character, but retains its position within the message.
A class of cipher that is occasionally used as a Gimmick in Thematic Cryptic Crosswords. In a substitution cipher, each letter of the alphabet is consistently replaced by another. The replacement is usually systematic: for example, involving a constant letter shift (a Caesar shift cipher) or a keyword as in this example using the key phrase "Judgment of Paris".
a cipher that replaces each plaintext symbol with another ciphertext symbol