batman vs houseboy

batman

noun
  • A servant or valet to a military officer. 

  • A unit of weight established in 1931 equal to 10 kg. 

  • A Turkish unit of weight varying by location, time, and item from 2–8 okas (about 2.5–10 kg). 

  • A personal assistant or supporter. 

verb
  • To climb up or down a rope free hand (i.e. as Batman does). 

  • To act as a batman, wait on an officer. 

houseboy

noun
  • A non-white adult male domestic servant. 

  • A young male domestic servant, especially in a British colony in former times. 

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