big house vs mansion

big house

noun
  • Used other than figuratively or idiomatically: see big, house. 

  • A religious building of the Delaware Indians, representing the cosmos. 

  • Prison, jail. 

mansion

noun
  • An individual habitation or apartment within a large house or group of buildings. (Now chiefly in allusion to John 14:2.) 

  • An astrological house; a station of the moon. 

  • An apartment building. 

  • One of twenty-eight sections of the sky. 

  • Any of the branches of the Rastafari movement. 

  • A large house or building, usually built for the wealthy. 

  • A luxurious flat (apartment). 

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