boy toy vs concubine

boy toy

noun
  • A gigolo or younger man who is sexually pursued by an older person. 

  • A toy meant to be played with by a boy. 

concubine

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

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

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

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