purring vs sibilant

purring

noun

  • A sound that purrs. 

  • Synonym of shin-kicking 

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 purring and sibilant occurred in a corpus of books? (source: Google Ngram Viewer )