susurrus vs zizz

susurrus

noun

  • A whispering or rustling sound; a murmur. 

zizz

noun

  • A buzzing or whizzing sound. 

  • A nap or sleep. 

verb

  • To take a nap. 

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