dungeon vs oubliette

dungeon

noun
  • An underground prison or vault, typically built underneath a castle. 

  • A room dedicated to sadomasochistic sexual activity. 

  • An area inhabited by enemies, containing story objectives, treasure and bosses. 

verb
  • To imprison in a dungeon. 

oubliette

noun
  • A dungeon only accessible by a trapdoor at the top. 

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