haunting vs mnemonic

haunting

adj
  • Remaining in the mind; not easily forgotten. 

noun
  • A particular instance of haunting; a ghostly habitation. 

mnemonic

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

  • Of or relating to memory. 

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

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. 

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