belfry vs bell tower

belfry

noun
  • A part of a large tower or steeple, specifically for containing bells. 

  • A shed. 

  • A tower or steeple specifically for containing bells, especially as part of a church. 

bell tower

noun
  • A tower in which a bell (or set of bells) is hung; a belfry. 

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