mnemonic vs pro memoria

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”). 

pro memoria

noun
  • A memory-aid; a reminder or memorandum, especially a book or document serving this purpose. 

  • A document circulated in a meeting or summit for discussion purposes. 

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