babyish vs sibilant

babyish

adj
  • For a young man, he has the most babyish voice I've heard. 

  • Like or suitable for a baby or a young child; childish 

sibilant

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

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

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