glasshouse vs prison camp

glasshouse

noun
  • A military prison. 

  • A greenhouse, especially one for commercial use. 

  • A building where glass or glassware is manufactured. 

prison camp

noun
  • A low-security federal prison. 

  • A camp in which either prisoners of war or political prisoners are interned. 

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