baptism vs christening

baptism

noun
  • A Christian sacrament, by which one is received into a church and sometimes given a name, generally involving the candidate to be anointed with or submerged in water. 

  • A similar ceremony of initiation, purification or naming. 

christening

noun
  • The Christian sacrament at which someone, usually a child, is baptized and given a Christian name. 

  • Any instance of someone's or something's being christened. 

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