catchword vs mnemonic

catchword

noun
  • A word under the right-hand side of the last line on a book page that repeats the first word on the following page. 

  • A word or expression repeated until it becomes representative of a party, school, business, or point of view. 

  • The last word of a speech, serving as a cue for the next speaker. 

mnemonic

noun
  • Something (especially a series of ideas, letters, words, etc.) used to help in remembering a thing; a memory aid. 

  • The human-readable, textual form of an assembly language instruction, not including operands. 

adj
  • Of or relating to memory. 

  • Especially of a series of ideas, letters, words, etc.: intended to help in remembering. 

  • Of or relating to mnemonics (“the study of techniques for remembering anything more easily”). 

How often have the words catchword and mnemonic occurred in a corpus of books? (source: Google Ngram Viewer )