blackboard vs hall

blackboard

noun
  • A large flat surface, finished with black slate or a similar material, that can be written upon with chalk and subsequently erased; a chalkboard. 

verb
  • To use a blackboard to assist in an informal discussion. 

hall

noun
  • A corridor; a hallway. 

  • A meal served and eaten at a college's hall. 

  • A college's canteen, which is often but not always coterminous with a traditional hall. 

  • A meeting room. 

  • A building providing student accommodation at a university. 

  • A living room. 

  • A place for special professional education, or for conferring professional degrees or licences. 

  • The principal room of a secular medieval building. 

  • A manor house (originally because a magistrate's court was held in the hall of his mansion). 

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