murmuring vs sibilant

murmuring

noun

  • A sound that murmurs. 

  • A complaint against something. 

sibilant

noun

  • A consonant having a hissing or hushing sound such as the s or sh in sack or shack. 

adj

  • Characterized by a hissing or hushing sound such as the s or sh in sack or shack. 

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