bathhouse vs onsen

bathhouse

noun
  • A building with baths for communal use. 

  • A building where swimmers can change clothes. 

  • A business with bath-like facilities, which chiefly serves as a place for sexual encounters, especially among men. 

onsen

noun
  • A Japanese-style resort hotel at a natural hot spring, offering on-site bathing. 

  • A (Japanese) hot spring. 

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