powder room vs thunderbox

powder room

noun
  • Synonym of ladies' room: a lavatory intended for use by women. 

  • A room used to powder hair and wigs. 

  • A room used to store gunpowder, particularly (historical) on a ship equipped with cannon. 

  • Synonym of half bath: a small room with a toilet and sink but no bathtub or shower. 

thunderbox

noun
  • Any lavatory or toilet, especially a rudimentary outdoor latrine or toilet, or an outhouse. 

  • A box of metal balls which is shaken to create a thunder sound effect. 

  • A chamber pot enclosed in a box; a portable commode. 

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