/ Dictionary / Index S substitution cipher: Meaning and Definition of Find definitions for: substitu'tion ci"pher Pronunciation: [key] — Cryptography. Cryptography. a cipher that replaces letters of the plain text with another set of letters or symbols. Cf. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. substitute substitution reaction Related Content Daily Word Quiz: paradox Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language