sibilant vs susurration

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. 

susurration

noun

  • A low and indistinct whispering sound; a murmur. 

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