birthday suit vs nudism

birthday suit

noun
  • Nakedness, unclothed skin; an exposure of a human's natural anatomy without clothing. 

  • Used other than figuratively or idiomatically: see birthday, suit. 

nudism

noun
  • The belief in or practice of going nude in social, nonsexualized and frequently mixed-gender groups specifically in cultures where going nude in the social situation is not the norm. 

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