mau-mau vs oppress

mau-mau

verb
  • To menace through intimidating tactics; to intimidate, harass; to terrorize. 

oppress

verb
  • To keep down by unjust force. 

  • To make sad or gloomy. 

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