concubine vs sugar baby

concubine

noun
  • A sexual partner, especially a woman, to whom one is not or cannot be married. 

  • A slave-girl or woman, kept for instance in a harem, who is held for sexual service. 

  • A woman who lives with a man, but who is not a wife. 

sugar baby

noun
  • The younger recipient (usually female or a bottom) of interest from a sugar daddy or sugar mama, especially financial and romantic in an intergenerational relationship 

  • A term of endearment; sweetheart. 

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